DK144365B - PACKAGING WRAPPING MATERIAL CONSISTING OF A PREPARATION OF ALUMINUM WRAP WITH COATED POLYOLEFIN FILM - Google Patents

Description

(19) DENMARK (^}

| J | (12) PUBLICATION WRITING (11) 144365 B

DIRECTORATE OF THE PATENT AND TRADEMARKET SYSTEM

(21) Application No. 1481/72 (51) Int.CI.3 B 32 B 15/08 (22) Filing date 28 Mar. 1972 B 65 D 6 5 / Λ 0 (24) Running day Mar 28 1972 (41) Aim. available Oct. 3 1972 (44) Submitted Mar 1 1982 (86) International application # - (86) International filing day (85) Continuation day - (62) Master application no -

(30) Priority 2 Apr 1971 »4836/71, CH

(71) Applicant SWITZERLAND ALUMINUM AG »3965 Chippis, CH.

(72) Inventor Erich Hoefling, CH: Eugen Werner, CH: Siegfried

Bloeck, CH.

(74) Associate Engineer Giersing & Stellinger.

(54) Packaging film material consisting of aluminum foil with a lacquer layer and then adhered to polyolefin film.

The invention relates to a packaging film material for articles containing free carboxylic acids and / or alcohols, e.g. meat dishes, liver pastries and oil-prepared fish dishes, which material consists of the following successive layers: an aluminum foil, a lacquer layer, a polyurethane adhesive layer and a polyolefin foil having a thickness of 0.012 - 0.05 mm.

2 In practice, it turns out to be extremely difficult for laminate materials of aluminum and polyolefins for packaging to match the properties of the adhesives, while at the same time taking into account the diverse requirements of practice and meeting all requirements in this regard. for adhesion strength and density. This is mainly due to the fact that the surfaces of polyolefin film and aluminum foil adhesive have very different properties. In addition, the polyolefin films - which are mostly polypropylene - are not absolutely impermeable, nor that the adhesives in this regard constitute an effective barrier. In disadvantageous active ingredients are the free carboxylic acids. They are able to penetrate the plastic film and the adhesive layer and, due to their chemical properties, can lead to reactions with the aluminum oxide's natural oxide coatings, thereby reducing the adhesion pressure in the adhesive / aluminum interface. This is especially the case during the sterilization process, which is due to the high temperatures encountered in this process. A consequence of this is a separation between polyolefin and aluminum (de-lamination). The fillers that contain free carboxylic acids are mainly meat dishes, liver pastries and fish-prepared fish products. They do not in themselves corrode on the aluminum, but lead to the aforementioned de-lamination, which is disturbingly noticed, especially when opening the packaging.

It has now been found that by means of suitable multilayer structure of the intermediate layer laminate foil it is possible to control its properties so that the laminate foil meets all requirements.

In the case of a packaging material of the type mentioned initially, this is achieved according to the invention in that the lacquer layer is a laminate layer of epoxy resin containing a phenol aldehyde resin and having a surface weight of 0.5 - 2 g / cm 2, which, before application of the adhesive layer, is cured on the aluminum foil by cross-linking with the phenol aldehyde resin using elevated temperature, e.g. 250-270 ° C for 0.5 - 3 minutes.

Such an epoxy resin layer exhibits a very strong adhesion to both the aluminum foil and the polyurethane adhesive layer and effectively prevents the entry of carboxylic acids to the aluminum foil.

The effect obtained by the invention in comparison with known laminates without an intermediate layer between the aluminum foil and the polyurethane adhesive layer is illustrated in the drawing in the diagrams shown in Figures 1-3.

Figures 1 and 2 show the measured peel strengths of the compared laminates after sterilization at 125 ° C for 30 minutes and 6 months storage in an aqueous solution of acetic acid and ethyl alcohol, respectively, with the abscissa deposited concentration. It will be seen that the laminate according to the invention does not show any reduction in the peel strength, even with long-term action of acetic acid or ethyl alcohol in high concentration, respectively.

A similar result is obtained by the examination of the resistance of the laminates compared to different edible fats during sterilization illustrated in Fig. 3. As an ordinate, the peel strength and abscissa are assigned the acid numbers of the fats in question in mg KOH per day. grams of fat. It will be seen that the packaging material according to the invention exhibits consistently high peel strengths, while the known films exhibit lower values, which also decrease strongly with the acid number of the fat in question.

The increased adhesion of the film layers obtained by the invention, even after prolonged action of carboxylic acids and other substances in the packaged goods, compared to known film materials with an intermediate lacquer layer can best be seen by comparison with a known film material (US patent 3,502,541). , in which an interlayer for improving the adhesion between the aluminum foil and the adhesive layer uses a semi-cross-linked two-component epoxy-amine system.

These known laminates have a peel strength before sterilization of 215 - 310 g / cm 2 and after sterilization of 170 - 230 g / cm 2, while a laminate according to the invention exhibits a peel strength of 470 - 600 g / cm 2 after sterilization in water. This improvement can be attributed to the fact that the film material according to the invention makes use of a highly cross-linked epoxy-phenolic lacquer intermediate, which has a much greater chemical resistance than the previously used intermediate layers.

Epoxy resin-phenolic resin varnishes are known and consist of a mixture of epoxy resin (condensation product of epichlorohydrin and diphenylol propane) and phenolic resin (phenol-formaldehyde condensation product), wherein the epoxy resin is crosslinked by the phenolic resin. The polyurethane adhesives are also known in the art; they are due to cross-linking of isocyanates with carboxyl or hydroxyl or both carboxyl and hydroxyl-containing compounds.

The packaging material may be laminate sheets, e.g. for bags and soft packs, as well as laminate tapes for deep-drawn containers and cans of all kinds. An epoxy resin-phenolic resin layer of more than 2 g / m2 (a layer of 1 g / m2 has about a thickness of 1 µm) has an adverse effect as the adhesion deteriorates.

Although it is known in practice in the case of canning can manufacture that paint layers of 5 - 7 pm are necessary for impeccable corrosion protection of a metal container for food, it was found here against expectation 4 144365 that already using layer thicknesses of less than 2 of an epoxy resin-phenolic resin can be adequately protected against de-lamination phenomena. This allows, for the first time, the use of biaxially stretched or oriented films of low thickness to produce deep-drawn can bodies.

Preferred layer thicknesses for the epoxy resin intermediate layer of the packaging material of the invention are the following: Aluminum foil 0.05 - 0.15 mm, polyurethane adhesive layer 0.004 - 0.012 mm, polyolefin film 0.0125 - 0.075 mm.

Furthermore, thus produced laminate material exhibits peel strengths which are not only the corresponding strengths obtained from known foil materials, but which also exceeds the tensile strength of the plastic film so that it can no longer be separated from the aluminum with the mechanical auxiliary film. . Therefore, containers made of such material can also be demolished to form a defined aperture without separating aluminum and plastic on a larger surface.

The mentioned advantages also apply to a laminate material in which the aluminum surface was subjected to a degreasing or chemical pretreatment prior to bonding. That is, applying the additional lacquer layer in addition to all the other benefits - against the past experience of practice - makes a careful and costly degreasing or chemical pretreatment or both of these processes on the aluminum foil superfluous.