CA2413740A1

CA2413740A1 - Composite system consisting of a support material and at least one layer containing a barrier material

Info

Publication number: CA2413740A1
Application number: CA002413740A
Authority: CA
Inventors: Ulrich Moosheimer; Rolf Kippenhahn; Andreas Wasche; Silke Kleinheins; Axel Borcherding; Thomas Luck
Original assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Current assignee: Individual
Priority date: 2000-07-04
Filing date: 2001-07-02
Publication date: 2003-01-02
Also published as: DE10032361A1; EP1296826A1; WO2002002315A1

Abstract

The invention relates to a composite system consisting of a support material and at least one barrier layer. At least two layers are provided on the support material, at least one layer being a protein layer and at least one other layer consisting of an inorganic material and/or an organic monomer.

Description

A COMPOSITE SYSTEM OF A SUBSTRATE MATERIAL AND AT LEAST ONE
LAYER CONTAINING A BARRIER MATERIAL
The invention concerns a composite system of a support material and at least two layers arranged on the support material, where one layer is a protein layer and the other layer is a layer of an inorganic material and/or an organic monomer.
Currently for the most part metals (for example aluminum and tinplate), glass, polymers (for example EVOH or PVDC), polymers vapor coated with thin metal or oxide layers, or the corresponding metal combinations are used as barrier materials.
For use of plastics and paper/cardboard in the area of packaging foodstuffs, pharmaceutical and industrial products, the barrier action against permeation of gases, water vapor, flavorings and chemicals must be very high and must be improved by up to four orders of magnitude over the starting substances. On an industrial scale the barner effect is achieved by applying barrier layers, and only high grade surfaces, i.e., ones with low roughness are suitable for the coating, in each case according to the coating process.
As an alternative, the rough surfaces of plastic films are made smooth by acrylic coatings.
Industrial vacuum coating methods using inorganic materials, wet coating methods and lamination are used as methods for coating.
Using vacuum technology plastic films are vapor coated mainly with 10-100 nm thick aluminum, silicon oxides or aluminum oxide layers and then laminated to other plastic films using traditional lamination adhesives. The thickness of the adhesive film is for the most part a few micrometers.
A composite system of a support material and at least two layers arranged on a support material, where at least one barner layer contains an inorganic%rganic hybrid polymer (Ormocer~ layer), and at least one other layer is a support layer or another barrier layer, is now described in EP 0 792846. With this layer system it was found that there is a synergistic effect between the inorganic layer and the Ormocer~
layer, which acts as a barrier. The oxygen barrier in this case is below the measurement limits of the oxygen permeability measurement device, 0.05 cm3/m2~daybar, measured at 23°C and SO% relative humidity (U. Moosheimer, H.-C. Langowski, A. Melzer, "Permeation Process Through Vacuum Web Coated Films," Pmc. Of the 13'~ International Conference on Vacuum Web Coating, Tucson, 1999. Bakish Material Cooperation, Englewood, p.
102, 1999).
However, it is disadvantageous with this method that the application of the' Ormocer~ coating in the form of a lacquer coating is very costly and because of the high material costs the coating is expensive, so that the corresponding product can be offered only at very high prices. For this reason this layer system has up to now not gained acceptance in the field of foodstuff packaging in practice.
Based on this, the task of this invention is proposed, a composite system for support materials that has the required barrier effect for gases (especially oxygen), water vapor, flavorings and chemicals and that at the same time should be cheap to manufacture and, if possible, be biodegradable.
For use in the field of packaging foodstuffs and pharmaceutical products there must also be the corresponding legal approvals.
The task is solved by the characteristic traits of Claim 1. The subordinate claims point out advantageous further developments.
Thus it is proposed in accordance with the invention that at least one layer system, which consists of at least one protein layer and a layer that contains inorganic materials and/or organic monomer be applied to the support material.
With this solution in accordance with the invention a significant improvement of the barrier effect of plastics or films, three dimensional bodies, bottles, paper/cardboard, cellulose film and starch-based films is achieved. The invention is based on the structural physical modification of the native protein structure by a water-based formulation of the protein-containing barrier layer in the form of a gel-like structure. Thus, with the invention it can be possible to obtain water vapor-stabilized multilayer packaging material based on biopolymers without the base properties of biodegradability being disadvantageously reduced. The invention thus is a cheap and biodegradable barrier coating that in combination with, for example, biodegradable layers (polylactic acid, regenerated cellulose film, polycaprolactone, biodegradable polyester) and preferably layers of metals, oxides, semiconductors preferably applied by vacuum technology is even excellently suitable for the production of biodegradable superbarrier materials.
The advantage of the protein coating additionally consists in the fact that the costs for the protein layer are low (under 0.02 DM/m2) and that food law approval already exists. The layer can also be processed without organic solvents (it is water based). It should further be emphasized that the coating thus consists of renewable raw materials that are biodegradable as well as self sticking or adhesive.
In a preferred variation the coating is also water soluble, where removal from the coating from the support and cleaning of it can be realized particularly simply. In this way recycling of the support is technically simplified.
Preferably, the composite system has an oxygen permeability of less than 0.1 cm3/m2~daybar, measured at 23°C and 50% relative humidity.
Especially preferably, the oxygen permeability of the composite system is less than 0.05 cm3lmZ~daybar.

Basically, there are two variations for the composite system in accordance with the invention. In the first variation the composite system is structured so that the protein layer is applied directly to the support material and the layer that contains the inorganic material and/or organic monomer lies on the protein layer. The advantage of this variation should be seen in that the protein coating can be used at the same time to smooth rough substrates like paper, cardboard or cellulose film, so that it is very suitable for subsequent coating with the layer of inorganic materials and/or organic monomers. In this case the protein film functions as barrier layer and smoothing layer.
In the secondary variation the layer of inorganic material lies directly on the support material and the protein layer is arranged on top of it and acts as a barrier and cover or laminating layer.
Of course, the solution in accordance with the invention also encompasses layer systems in which still more layers are applied to the composite system of protein layer and inorganic layer and/or organic monomer layer. It is also possible to arrange yet another layer between the support material and the composite system. However, what is important in accordance with the invention is in all cases the composite of protein film and inorganic layer and/or organic monomer layer, since the synergistic effect arises through this composite. From the material standpoint the invention encompasses, in the case of the support material, substrates like plastic (for example PET, BOPP, PP, OPA, LDPE, LLDPE, HDPE, PE, PA, PVC), paper, cardboard, paperboard, PLA, cellulose film and starch based films. The support material preferably has a thickness of 1 Eun to 500 Eun, especially preferably 4 to 60 Eun.
The support material can also be in a three dimensional form, for example bottle-shaped, hollow objects or tubular shaped. Examples in this case are PET
bottles or plastic tubes.
The inorganic materials are preferably metals and/or metal oxides and/or semiconductors. Examples here are aluminum oxides, magnesium oxides, cerium oxides, silicon oxides like silicon monoxide or silicon dioxide, carbosilicates, titanium oxides like titanium dioxide or titanium (3) oxide or titanium monoxide, yttrium oxides, zirconium oxides like zirconium monoxide or mixtures of these. This layer, which contains metals or metal oxides and/or semiconductors, is preferably applied by vacuum technology. In this way an exact layer application is possible. Vacuum deposition takes place so the layer thickness lies in the range from 5 nm to 500 nm, especially preferably nm to 100 nm.
Monomers with low molecular weight which form a molecular solid upon being vapor deposited and thus under nonnal conditions form solid stable layers are used as organic monomers here. For instance, triazines like melamine and the like, for example, only require an evaporation temperature of about 200°C. Substances of homogeneous molecules, which go through the evaporation operation intact and then reform a crystalline layer, are advantageously used as organic monomers. Molecules with molecular weight up to 1200 daltons are advantageously used. Triazines, especially 1,3,5-triazine or its salts or a mixture of these can be used. In particular melamine, ammeline, ammelide, cyanuric acid, 2-ureidomelamine, melam, melem, melon or melamine salts like melamine cyanurate, melamine phosphate, dimelamine pyrophosphate or melamine polyphosphate or functionalized melamine such as hexamethoxymethyl melamine or acrylate-functionalized melamine or mixtures of these are suitable as organic monomer.
The protein layer preferably contains proteins of plant origin. Especially preferred among these are proteins contained in lupines, soy, peas, flaxseed, wheat, maize and/or rape.
The layer can also consist of proteins of animal origin, where gelatins, casein, milk proteins and/or their derivatives are especially preferred.
The layer thickness of the protein layer is 1 ~m to 50 l.un, preferably 5 Eun to 30 lun, where the layer is applied to the substrate as a thin film. The protein layer is in this case obtained from a formulation whose dry matter content is preferably between 10 and 50 wt%, especially 20-30 wt%. Because of this low solids content, application of this layer in the form of a film is easily possible.
The formulation for production of the protein layer contains, in the dry matter fraction, preferably a pmtein fraction of at least 50 wt%, especially preferably at least 80 wt%.
The described composite system has proved itself especially for application to three-dimensional bodies, for example hollow objects, a bottles of polyethylene or PET.
It is possible with the composite system in accordance with the invention to coat PET
bottles and produce a barrier action against oxygen, C02 and flavorings, so that even beverages like beer, soft drinks, wine, can be packaged in such bottles.
The invention is described in more detail below by means of an embodiment example.
Examples PET film rolls (12 l.un) and BOPP film rolls (20 Eun) were coated with different amounts of plant protein formulation based on protein isolates from oil seeds (for example rapeseed, lupines, soy) or of animal origin (for example milk casein) by smooth roller application (40°C) on a laminating machine. In addition, PET
film (12 Vim) and PET film industrially vapor coated with SiOX (12 lun) were coated with a hand doctor blade (40 dun). Some protein solution examples are given in Table 1.
Solvent Softener Protein PH

4008 Water 37g Glycerol 115g Rapeseed 11,5 rotein concentrate 350 Water 37 Gl cerol 50 Pea rotein 10,5 350g Water 37g Glycerol 115g Lupine 10,3 protein concentrate 350 Water 37 Gl cerol 115 Wheat rotein11,3 230g Water + 7,5g Glycerol 80g Wheat protein3,8 225 Ethanol In all cases distilled water was used as solvent. The pH of the protein solutions was adjusted with NaOH for the alkaline iange (pH > 9) and with acetic acid for the acid range (pH < 4).
Drying took place by IR radiation. Figure 1 schematically shows the structure of the super barner to gases (oxygen, water vapor, flavorings). Paper substrates or the AUSiOX layer in Figure 1 moreover offer a protection against light (U~, for example, for oxidation-sensitive products. In Figure 2 the protein coating is used as a barner coating or lamination.
The results of the oxygen permeability measurements are summarized in the following table.
Film Application Coating 02 Permeability, Wei t m2 Hardenin 23C/SO%
r.H.
cm3/ m2d bar PET 12~ 1 5 1 80,6 91,6 PET 12w 2 1 27,3 32,4 PET 12 4 1 17,6 23 4 BOPP 20 1,5 1 32 5 41 8 BOPP 20 4 4 13,5 15,4 To establish if the protein coatings are barner coatings, the oxygen permeabilityt is determined on a 100 ~.m thick protein layer by the standard method. This can be calculated from the measured oxygen permeability values in combination with the measured application weight and gives an oxygen permeability of under 1 cm3/m2~daybar with respect to 100 Eun layer thicknesses, which corresponds to the barrier of the superbarrier coating Ormocer~ in accordance with EP 0 792 846.
Film Inorganic LayerBetter Coating 02 Permeability, 23C/SO% r.H.

cm3 / m2d bar PET A1 ORMOCER~ < 0,05 PET SiO, 0,38 PET SiO~ Protein < 0,05 PET SiO ~ Protein <0,05 The oxygen barner of a protein coating (here lupine protein) of SiOx-coated PET
films corresponds to that of an SiOx-coated film with Ormocer~ coating. In contrast to Ormocer~ the protein coatings are characterized by being free of solvents and soluble in hot alkalis, by biodegradability and by low manufacturing costs.
The following table gives a comparison of the oxygen permeability of variously coated PET films (hand blade, 40 Eun coating), where only pmteins of plant origin were used as proteins.
Film Barrier Coating 02 Permeability, 23C/50%

r.H. cm3/ m2d bar PET Lu ine isolate 49;7 PET SiOX/lu ine isolate < 0,05 PET Wheat alkaline -PET SiOx/wheat alkaline < 0 OS

PET Whea acid 41,0 PET SiOX/wheat, acid < 0,05 PET pea rotein 84,5 PET SiOX rotein < 0,05 PET . Ra eseed rotein 72,4 PET SiOX/ra seed mtein < 0 OS

Claims

1. A composite system of a substrate material and at least one barrier coating, which is characterized by the fact that at least two layers are arranged on the substrate material, where at least one layer is a protein layer formed by structural, physical modification of the native protein structure and at least one additional layer is a layer of an inorganic material and/or organic monomer.

2. A composite system as in Claim 1, which is characterized by the fact that the composite system has an oxygen permeability of less than 0.1, preferably less than 0.05 cm3/m2.day.bar.

3. A composite system as in at least one of Claims 1 or 2, which is characterized by the fact that at least one layer of an inorganic material and/or organic monomer is applied to at least one protein layer that is arranged directly on the substrate material.

4. A composite system as in at least one of Claims 1 or 2, which is characterized by the fact that at least one protein layer is arranged on at least one layer of an inorganic material and/or organic material that is arranged on the substrate material.

5. A composite system as in at least one of Claims 1-4, which is characterized by the fact that the substrate system is chosen from among synthetic and natural polymers like plastics, paper/cardboard, cellulose film and/or starch-based films, coated paper, polylactide and polyhydroxy fatty acid.

6. A composite system as in Claim 5, which is characterized by the fact that the substrate material has a thickness from 1 µm to 5 mm.

7. A composite system as in at least one of Claims 1-6, which is characterized by the fact that the substrate material is in the form of a three-dimensional body.

8. A composite system as in at least one of Claims 1-7, which is characterized by the fact that the layer of inorganic material contains a metal and/or a metal oxide and/or a semiconductor.

9. A composite system as in Claim 8, which is characterized by the fact that the layer contains aluminum oxides, magnesium oxides, cerium oxides, hafnium oxides, tantalum oxides, silicon oxides like silicon monoxide or silicon dioxide, titanium oxides like titanium dioxide or titanium(3) oxide or titanium monoxide, yttrium oxides, zirconium oxides like zirconium monoxide, or mixtures thereof.

10. A composite system as in at least one of Claims 1-9, which is characterized by the fact that the inorganic layer has a thickness between 5 and 500 nm, preferably 10 and 200 nm, preferably 10 and 100 nm.

11. A composite system as in at least one of Claims 1-10, which is characterized by the fact that the protein layer contains proteins of plant origin, for example from lupines, soy, peas, flaxseed, maize, wheat, sunflower and/or rape.

12. A composite system as in at least one of Claims 1-10, which is characterized by the fact that the protein layer contains proteins of animal origin, for example of gelatin, casein, milk proteins and/or their derivatives.

13. A composite system as in at least one of Claims 1-12, which is characterized by the fact that the protein layer has been applied as a thin film with a layer thickness from 1 µm to 100 µm, preferably 1 µm to 50 µm.

14. A composite system as in at least one of Claims 1-13, which is characterized by the fact that the protein layer has been obtained from a formulation with a dry matter content between 5 and 50 wt%, preferably 10-30 wt%.

15. A composite system as in at least one of Claims 1-14, which is characterized by the fact that the protein layer has been obtained from a formulation with a protein fraction in the dry matter fraction of at least 50 wt%, preferably at least 80 wt%.

16. A method for producing composite systems with barrier properties to oxygen and/or water vapor by coating a substrate material by means of the following steps:
a) application of a layer of inorganic material and/or organic monomer and b) application of a protein layer formed by structural, physical modification of the native protein structure, where the sequence of steps (a) and (b) is arbitrary.