EP0067763B1 - Process for making multilayer structures - Google Patents

Description

The present invention relates to a process for manufacturing multi-layer complexes, intended in particular for closing plastic packaging such as, for example, bottles.

In this definition of the invention, the term “multilayer complex” is understood to mean a complex composed of at least two layers.

It is known at present to use, for closing hollow bodies made for example of plastic material, or any other packaging, round capsules or lids or of any shape, cut from multilayer sheets, composed of a film of aluminum and at least one layer of plastic, which seal said packages. The plastics generally used to constitute these closure caps are polyethylene, polypropylene, polyvinyl chloride or polystyrene, or combinations of these materials; the packaging is closed off by said capsule by adhesion of the multilayer complex and of the packaging by heat-sealing.

Depending on the plastics used, the multilayer sheets have a layer of adhesive located between the aluminum film and the layer of plastic.

They can also be constituted, as described in French patent No. 1,594,448, of which the Applicant is the holder, by an aluminum film and a layer of polyethylene containing, grafted, an unsaturated carboxylic acid, such as the acid acrylic.

Using capsules made from such multilayer complexes, heat-sealed on the packaging under the appropriate conditions, a tight seal is generally obtained, essential for the good preservation of the product packaged in the packaging.

However, it may happen that the films accidentally separate from each other, and that a tight closure is no longer obtained, which naturally affects the good preservation of the packaged product.

This phenomenon is called delamination and the causes are poorly understood.

US-A-3,783,062 mentioned that water and water vapor have an important role in the adhesion of the layers of a laminate and it is proposed to increase the resistance to delamination of certain laminates, produced by heating the surface of a sheet of a thermoplastic material with a flame and applying the heated face of this sheet against another sheet under pressure, by incorporating steam into the gaseous fuel used to produce the flame.

The Applicant has now found a way to overcome the drawbacks of the complexes mentioned above by applying to the aluminum foil a treatment with water brought to a temperature above about 60 ° C.

It further established that the adhesion of the polymer layer on the aluminum film was improved by this treatment.

In addition, it managed to adhere to the aluminum film a layer of a particular polymer, without using an adhesive, which had not been possible until now.

An object of the present invention is therefore to improve the adhesion of a polymer layer on an aluminum film and thus to avoid delamination of multilayer complexes.

Another object of the invention is to obtain direct adhesion of a layer of polymer to an aluminum film, without the interposition of an auxiliary agent.

To this end, the subject of the invention is a method of manufacturing a multilayer complex intended in particular for closing packaging, said complex comprising an aluminum film secured to at least one layer of polymer composed of a polymer of ethylene or of an ethylene copolymer or of a mixture of such copolymers, said process being characterized in that, to improve the adhesion of the layer of polymer to the aluminum film, one operates a treatment with water brought to a temperature above 60 ° C., said treatment being carried out either before the aluminum film is made integral with the polymer layer, on the surface of the aluminum film intended to come into contact with the polymer layer, either after making the aluminum film integral with the polymer layer, the treatment with water then being carried out on the complex itself. A water temperature less than or equal to 200 ° C can be considered sufficient.

Water can be in liquid form or in the form of vapor.

According to the invention, the polymer layer can be composed in particular of a copolymer of ethylene and of an unsaturated monoethylenic carboxylic acid. This polymer can in particular be obtained by polymerization of ethylene then grafting of a small amount, generally less than 5% by weight, of an unsaturated monoethylenic carboxylic acid; this acid can for example be acrylic or methacrylic acid.

The polymer layer can also be composed of high density polyethylene.

It can also be composed of a mixture of polymers, such as, for example, a copolymer of ethylene and of acrylic acid, as defined above, in mixture with a copolymer of ethylene and of vinyl acetate.

The aluminum film may have a thickness preferably between 30 and 80 microns.

The same applies to the thickness of the polymer layer when the polymer is, for example, polyethylene or a copolymer of ethylene and a non-monoethylenic carboxylic acid. saturated, as described above, or high density polyethylene.

According to the invention, the complex is prepared, after optional treatment of the aluminum film with water brought to a temperature above 60 ° C, then joining of the aluminum film and the polymer layer, by passing the film and layer, in a manner known per se, on heated transfer rolls.

Water treatment can be carried out after passing over the transfer rollers.

• - un film d'aluminium,
• - une mince couche (de 1 à 10 microns environ) d'un copolymère de l'éthylène et de l'acide acrylique, tel que défini précédemment, seul ou en mélange avec un copolymère du propylène et de l'acide acrylique ;
• - éventuellement une couche de polyéthylène ou de polypropylène.

The process according to the invention can also be used for the manufacture of particular two-layer or three-layer complexes comprising:

• - aluminum film,
• - a thin layer (from 1 to 10 microns approximately) of a copolymer of ethylene and acrylic acid, as defined above, alone or as a mixture with a copolymer of propylene and acrylic acid;
• - optionally a layer of polyethylene or polypropylene.

• a) la préparation d'une suspension du copolymère, seul ou en mélange dans un liquide organique,
• b) l'enduction du film métallique par la suspension du copolymère,
• c) l'élimination du liquide organique,
• d) la fusion du copolymère, de façon à obtenir une couche continue du copolymère sur le film métallique.

In this case, the complex is preferably prepared by a particular process comprising the following steps:

• a) the preparation of a suspension of the copolymer, alone or as a mixture in an organic liquid,
• b) coating the metallic film with the suspension of the copolymer,
• c) elimination of the organic liquid,
• d) melting the copolymer, so as to obtain a continuous layer of the copolymer on the metallic film.

The suspension of the copolymer can be obtained by dissolving the copolymer alone or as a mixture in an organic liquid, then by cooling the solution, said cooling preferably being rapid.

The coating of the aluminum film can be carried out by means known in the art. It can be done, for example, using a transfer roller.

The organic liquid contained in the suspension must then be removed from the coated metal sheet, by drying the support, for example by heating in a heating tunnel.

The aluminum film is then brought to a temperature sufficient for the compounds to be melted.

In the case where it is desired to obtain a three-layer complex, a layer of polyethylene or polypropylene can be joined to the polymer layer by passing over transfer rolls.

In the case of the preparation of these two- or three-layer complexes, the treatment with water is done before or after the layers are joined together.

The method according to the invention makes it possible to obtain complexes which delaminate only with very little difficulty. Indeed, the complexes prepared in a conventional manner, that is to say without the aluminum film being treated with hot water before their use, manage to delaminate.

This is the case, in particular, when, after heat-sealing on the containers, they are cooled by cold water.

The following examples are intended to illustrate the invention. They are not limiting.

Example 1

This example relates to delamination tests carried out by a bilayer complex composed of an aluminum film with a thickness of 50 microns and a film of ethylene acrylic acid copolymer with a thickness of 50 microns. also.

This copolymer was obtained by grafting on high density polyethylene (d = 0.960) of acrylic acid (about 1% by weight).

The aluminum film and the copolymer film are calendered at 220 ° C. between two cylinders.

Samples with a width of 10 mm, T and A are prepared from the complex thus obtained.

T samples, which are control samples, do not undergo any special treatment.

Samples A are brought into contact with steam at 120 ° C for 20 min.

The samples T and A are then immersed in water at 23 ° C.

The variation in the adhesion of the aluminum and copolymer films is then followed as a function of the soaking time in water at 23 ° C. The adhesion tests are of the “peeling” type and consist in measuring the adhesion force of the copolymer and aluminum films, when they are subjected to opposite tensile forces, the complex being kept perpendicular to the acting forces.

The adhesion "peeling", which is the average force per unit of width of test piece necessary to cause separation of the two films is measured when the two films are separated at a uniform speed of 120 mm / min.

Tests were carried out over a period of four weeks.

For samples T, the adhesion before soaking in water at 25 ° C is close to 400 gf / 10 mm. It decreases with the soaking time and reaches, after about 5 hours, a value close to 200 gf / 10 mm. For samples A, the adhesion close to 800 gf / 1 mm remains constant.

Example 2

This example relates to delamination tests on complexes B1 and B2 similar to the complex A of example 1.

The complexes B1 and B2 are soaked in water brought to different temperatures: 80 ° C and 100 ° C.

The soaking time was varied from 15 minutes to 2 hours 45 minutes. Then, in the same way as in Example 1, adhesion tests were carried out by comparing them to the tests carried out with the control T complexes.

For complexes B1 (treated in water at 80 ° C), the adhesion, after 24 hours of soaking in water at 23 ° C, increases with the treatment time in water at 80 ° C . It goes from around 250 gf / 10 mm for 1/4 hour of treatment to 500 gf / 10 mm for 2 3/4 hours.

For B2 complexes (treated in water at 100 ° C), the adhesion, after 24 hours of soaking in water at 23 ° C, increases with the treatment time in water at 100 ° C. It goes from around 500 gf / 10 mm for 1/4 hour of treatment to 800 gf / 10 mm for 2 3/4 hours.

For samples T, the adhesion after 24 hours of soaking in water at 23 ° C, is about 200 gf / 10 mm.

The adhesion of the complexes prepared by the process according to the invention is therefore much better.

Example 3

This example relates to delamination tests on C complexes similar to those of Examples 1 and 2.

However, these complexes C are prepared from an aluminum film previously treated with water at 100 ° C. The soaking time was varied from 15 seconds to 20 minutes. The two-layer complexes C were then produced in the same way as in Example 1, and identical adhesion tests were carried out by comparing them with the tests carried out with the control complexes T.

The adhesion, after 24 hours of soaking in water at 23 ° C, increases with the time of pre-treatment of aluminum in water at 100 ° C. After 30 seconds of treatment, it is approximately 300 gf / 10 mm; after 2 minutes, it is approximately 500 gf / mm and, after 10 minutes, it is greater than 800 gf / 10 mm.

For samples T, the adhesion after 24 hours of soaking in water at 23 ° C is approximately 200 gf / 10 mm.

The adhesion of the complexes prepared by the process according to the invention is therefore much better.

Example 4

This example relates to delamination tests carried out on a bilayer complex D composed of an aluminum film with a thickness of 50 microns and a film with a thickness of 50 microns of high density polyethylene (d = 0.960), molecular weights by weight Mw = 110,000 and by number Mn = 13,000.

Attempts have been made to adhere the aluminum and high density polyethylene films, without prior treatment of the aluminum with water, by calendering at 220 ° C. Films do not adhere.

Complex D is then produced in the same way, but after treatment of the aluminum film for 20 minutes in water at 100 ° C. A peeling test as described above is carried out on complex D.

A value of 100 gf / 10 mm is obtained. After soaking the complex in water at 23 ° C for 24 hours, the same result is obtained.

The method according to the invention therefore makes it possible to directly adhere a film of high density polyethylene to an aluminum film, which is impossible otherwise.

Claims (11)

1. A process for manufacturing a multilayer structure intended more particularly to be used for sealing packages, said structure comprising an aluminium film integral with at least one polymer layer formed from an ethylene polymer or from an ethylene copolymer or from a mixture of such copolymers, said process being characterized in that, in order to improve the adhesion of the polymer layer to the aluminium film, a treatment is applied using water heated to a temperature greater than 60⁰C, said treatment being carried out either before the aluminium film is secured to the polymer layer, on the surface of the aluminium film intended to come into contact with the polymer layer, or after the aluminium film has been secured to the polymer layer, the water treatment then being carried out on the structure itself.

2. The process according to claim 1, characterized in that the temperature of the water is less than or equal to 200 °C.

3. The process according to one of claims 1 and 2, characterized in that the water is in the liquid phase.

4. The process according to one of claims 1 and 2, characterized in that the water is in the vapor phase.

5. The process according to one of claims 1 to 4, characterized in that the polymer is a copolymer of ethylene and of an unsaturated monoethylene carboxylic acid.

6. The process according to claim 5, characterized in that the unsaturated monoethylene carboxylic acid is acrylic acid.

7. The process according to one of claims 1 to 4, characterized in the the polymer layer is formed from high density polyethylene.

8. The process according to one of claims 5 to 7, characterized in that the structure is formed of an aluminium film having a thickness between 30 and 80 microns and in that the polymer layer has a thickness between 30 and 80 microns.

9. The process according to one of claims 1 to 4, characterized in that the polymer layer is formed by a mixture of a copolymer of ethylene and of acrylic acid and a copolymer of ethylene and vinyl acetate.

10. The process according to one of claims 5 and 6, characterized in that the structure is prepared by a process comprising the following steps :

a) preparation of a suspension of the copolymer alone or in a mixture, in an organic liquid,

b) coating of the metal film by means of the copolymer suspension,

c) elimination of the organic liquid,

d) melting of the copolymer so as to obtain a continuous layer of the copolymer on the metal film,

e) a possible additional step consisting in securing the copolymer layer to a polyethylene or polypropylene layer.

11. Structures prepared by a process according to one of claims 1 to 10.