WO1999012829A1

WO1999012829A1 - Packaging material

Info

Publication number: WO1999012829A1
Application number: PCT/SE1997/001508
Authority: WO
Inventors: Lennart Stolpe; Inga-Stina ÅKERBLOM
Original assignee: Peterson Scanproof Aktiebolag
Priority date: 1997-09-09
Filing date: 1997-09-09
Publication date: 1999-03-18
Also published as: AU4729697A

Abstract

A packaging material with extremely low permeability to oxygen is characterised in that it consists of or comprises a layer (1) of a paper which per se has a low permeability to oxygen, and that said paper (1) is coated with and/or is impregnated with any oxygen scavenging agent (2) (getter) which belongs to the group of agents which comprises organic acids and esters of organic acids.

Description

PACKAGING MATERIAL

TECHNICAL FIELD The invention relates to a packaging material with an extremely low permeability to oxygen.

BACKGROUND OF THE INVENTION

Products that shall be packaged are often oxygen-sensitive. This is particularly true for foods in which microbiological activity increases, upon which certain vitamins are decomposed and fats turn rancid and are discoloured by the action of air oxygen. Therefore, for many food- stuffs completely oxygen impermeable materials are used, for example, glass and metal. However, it is often desirable that the packaging material has a high degree of flexibility and other features which compel the packaging designer to use paper or plastic materials or combinations of such materials as packaging material. Some types of such materials may have a low oxygen permeability, e.g. so called greaseproof paper, as a single material or in combination with a plastic material, but for some of them the ability of the material to form a barrier against the oxygen is insufficient.

Many attempts have been made to compensate for the remaining permeability to air oxygen of flexible materials which are termed dense. One method is based on adding one or more oxidizable agents, into the packaging material or into the package, wherein the oxidizablbe agents will chemically bind the oxygen which succeed in penetrating the dense packaging material before the oxygen contacts the packaged product; i.e.. functions as a getter or scavenger for the oxygen. Papers laminated with layers containing oxygen binding materials are examples of packaging materials that have oxygen scavenging features, and "cushions" impregnated with oxygen scavenging material are examples of agents suggested to be contained in packages. Through the use of such materials and provisions, the permeation of air oxygen of the package is compensated for and hence the actual life of the product or the time until the packed product is affected is increased.

There are examples of packaging materials as well as of agents intended to be included in packages, which are oxidizable and aim at binding the air oxygen which has penetrated all the way through the package to the product in the package. For example, U. S Patent No.: 5,049,624 discloses a packaging material with a laminate structure in which that layer of the laminate which is the outermost layer relative to the product that is packaged, has a comparatively low permeance for oxygen, while the inner layer contains oxygen- scavenging agents in the form of organic matters and a metal catalyser which catalyses an oxidation reaction of the organic matter. There are also examples of the use of inorganic, oxidizable agents. E.g., the U.S Patent No.: 4,769,175 describes the use of iron, iron powder and a halogen as an oxidizable system for the elimination of oxygen in packages.

All the described oxidizable agents in oxygen- scavenging materials according to prior art, however, are either expensive or difficult to manufacture and use. Often they are also synthetic, difficult to decompose and/or render the recycling of the packaging material more difficult, which is a drawback from an environmental point of view. Usually they also have to be laminated with, or be contained in, other materials in order to function as oxygen scavengers and also in order not to contaminate the packaged product. Often they are also comparatively inflexible, which means that they do not have features harmonising with paper materials, or they consist of oxidizable plastic films or laminated plastic films, if they do not consist of other laminated materials which are difficult to degrade and/or which render recycling difficult.

DESCRIPTION OF THE INVENTION The invention aims at reducing or substantially eliminating the above mentioned deficiencies of the existing materials containing oxygen scavenging agents. More particularly, it is an aim of the invention to provide a material which contains or which is covered with an oxygen scavenging agent, but which does not exhibit the said drawbacks or limitations. The material shall also be incorporable into or laminated with other materials if desired.

This and other objects can be achieved therein that the packaging material consists of or comprises a layer of a paper which per se has a low permeability to oxygen, and that said paper is covered with and/or is impregnated with any oxygen scavenging agent (getter), which belongs to the group of agents which comprises organic acids and esters of organic acids.

According to an embodiment, the agent consists of ascorbic acid, which in the form of a solution can be supplied in connection with the paper manufacturing, e g in a size press or by an airbrush or by means of any other technique known in paper manufacturing, suitably against both sides of the paper, so that the paper is impregnated with ascorbic acid at least to a certain depth. According to a second embodiment said at least any oxygen scavenging agent consists of agents which exhibit unsaturated fatty acid groups and/or contain unsaturated fatty acids. Preferably, the unsaturated fatty acid groups and/or fatty acids contain 14 to 26 carbon atoms, preferably 16 to 24 carbon atoms, and suitably 18 to 22 carbon atoms. Suitably, the unsaturated fatty acid groups are bound as esters, substantially in glycerine esters, such as triglycerides. A drying oil, such as linseed oil has turned out to be particularly suitable as a scavenger in combination with paper. The oxidisability of linseed oil is well known and is utilised when linseed oil is used as a binder in paints and lacquers, wherein the unsaturated compounds, i.e., compounds containing one or more double bonds, scavenge the air oxygen i.e., are oxidised, wherein they polymerise or set, or "dry". A drying/setting oil such as linseed oil, also further improves the impermeability of the paper physically wherein it also reduces the permeability to air oxygen. Besides, the oil maintains its oxygen scavenging ability long after the drying/setting/polymerisation process is finished.

Linseed oil consists mainly of glycerol esters, oleic acid and linolenic acid, but the exact composition depends on where the flax has grown and how the oil has been extracted from the seeds. Linoleic acid and linolenic acid are polyunsaturated fatty acids and bound mainly as esters, such as triglycerides, in the linseed oil.

Examples of natural, unsaturated fatty acids, which are conceivably used as oxygen scavenging agents according to the invention as such or bound as esters, are given in the following table 1.

Table 1.

The agents which are given in the table, suitably in the form of linseed oil can be applied on or in the substrate, i.e., the paper layer which per se has a low oxygen permeability, by applying it on the surface of the paper in the form of a solution in a suitable solvent or in the form of a dispersion in water. E.g. white spirit or toluene or any other organic solvent, which dissolves the oiL can be used as solvent in the first case. In the letter case, a synthetic tenside can be used as a dispersing agent, e.g. a mixture of 75% Berol OMA4 (trade name) from AKZO Nobel AB and 25% TO2 (trade name) from Bergvik Kemi AB, or a tenside manufactured from natural raw materials, e.g. pot ash soap.

Alternatively, an adapted addition of potassium or sodium hydroxide to the water in connection with the formation of the dispersion results in a partial saponification of the linseed oiL wherein the produced soaps contribute to the dispersion. The dispersion can also be applied to the stock through the addition of a dispersion according to the above prior to the paper manufacturing, wherein a cationic retention agent ought to be added, i.e., a polyamide amine resin, for example Kenores 1444 (trade name) from Eka Nobel AB, a polyacrylamide or a cationic starch in order to bring about an acceptable retention of the dispersed agent in the paper.

The said oxygen scavenging agents have proved to be particularly efficient when the paper layer belongs to the group of fat-proof and fat resistant papers, which include greaseproof paper, vegetable parchment, and imitation parchment (glassine). These types of paper are very impervious per se but not completely air-proof, wherein, however, the oxygen scavenging agent according to the invention eliminates or reduces to an acceptable level, through oxidation, the amount of oxygen which penetrates the paper.

The oxygen scavenging agent can be supplied to the stock or to the paper in the paper manufacturing machine at various points. The oxygen scavenging agent or agents may also be supplied to the paper in a separate impregnation or coating machine. The oxygen scavenging agent may be dissolved in water, which is the case when the agent is ascorbic acid, or dispersed e g in water as above.

Various methods known in the art can be employed for the coating or impregnation operation, such as e g spraying, immersion, doctoring, size press coating, and roller coating by means of smooth or engraved rolls, etc.

Further characteristic features and aspects of the invention will be apparent from the appending claims and from the following description and report of performed experiments.

BRIEF DESCRIPTION OF DRAWINGS

The drawings schematically show some conceivable packaging materials of the invention in cross section. The measures are not according to scale. In the drawings

Fig. 1 shows a greaseproof paper impregnated with ascorbic acid and covered with polyethene on both sides,

Fig. 2 shows the same as Fig. 1 and also a polyethene covered board layer,

Fig. 3 shows a greaseproof paper which has been treated with linseed oil on one side thereof, and

Fig. 4 shows a linseed oil treated greaseproof paper according to Fig. 3, which has been covered on both sides with polyethene and then laminated with a plastic covered board layer.

DETAILED DESCRIPTION OF THE INVENTION In the drawings, a greaseproof paper having the surface weight 50 g/m^ has reference numeral 1. Fig. 1 shows such a greaseproof paper 1, on the two sides of which has been supplied 0,5 ascorbic acid/ m², whereupon a 20 g/ m² thick polyethene layer 2. 3 has been extruded on each side. The ascorbic acid was supplied in the form of an aqueous solution, using a size press in the paper making machine for applying the solution, and was impregnated essentially in the paper layer. The manufactured material has been designated 4 in Fig. 1.

Fig. 2 shows a material 4 as above, which has been laminated with a board layer 5 which has a polyethene layer 6 on the opposite side thereof.

Fig. 3 shows a greaseproof paper 1 of the same type as in the other composite materials, which on one side thereof has been coated with linseed oil, 0,5 g/m². The linseed oil layer is designated 7. The treated material is designated 8.

Fig. 4 shows a material 8, which, when the linseed oil has "dried", has been covered with a polyethene covered board layer 5, 6. In the drawings, the same reference numerals consequently have been used for layers of the same type.

The materials 4 and 8 of the invention were tested and compared with a completely untreated greaseproof paper 1 and with greaseproof paper 1, which had not been treated with any oxygen scavenging agent, but which on each side had been covered with a polyethene layer with the surface weight 20 g/ m². The results are apparent from table 2.

Table 2.

Claims

1. Packaging material with extremely low permeability to oxygen, characterized in that it consists of or comprises a layer (1) of a paper which per se has a low permeability to oxygen, and that said paper (1) is coated with and/or is impregnated with any oxygen scavenging agent (2) (getter) which belongs to the group of agents which comprise organic acids and esters of organic acids.

2. Packaging material according to Claim 1, characterized in that the agent consists of ascorbic acid.

3. Packaging material according to Claim 1, characterized in that said at least one oxygen scavenging agent consists of agents which have unsaturated fatty acid groups and/or contains unsaturated fatty acids.

4. Packaging material according to Claim 3, characterized in that the unsaturated fatty acid groups and/or fatty acids have 14 to 26 carbon atoms, preferably 16 to 24 carbon atoms and suitably 18 to 22 carbon atoms.

5. Packaging material according to Claim 4, characterized in that the unsaturated fatty acid groups are bound as esters.

6. Packaging material according to Claim 5, characterized in that the esters are glycerine esters, preferably triglycerides.

7. Packagmg material according to Claim 6, characterized in that the unsaturated fatty acid groups comprise linoleic acid and/or linolenic acid groups and that the fatty acids comprise linoleic acid and/or linolenic acid.

8. Packaging material according to Claim 7, characterized in that the said oxygen scavenging agent consists of dried linseed oil.

9. Packaging material according to any of Claims 1-8, characterized in that the amount of oxygen scavenging agent amounts to between 0.05 and 5 g/m² paper layer, preferably between 0.1 and 4 g/m², suitably between 0.2 and 4 g/m².

10. Packaging material according to any of Claims 1-9, characterized in that the paper layer is laminated with at least any of the materials belonging to the group consisting of paper, plastic films, and cardboard.

11. Packaging material according to any of Claims 1-10, characterized in that the paper layer consists of a paper belonging to the group consisting of fat impermeable and fat resistant papers which comprises the group consisting of greaseproof paper, vegetable parchment, and imitation parchment (glassine).