EP2531419B1 - Process for easy opening of a foil sealed on the opening edge of a glass container and corresponding glass container - Google Patents

Abstract

The invention provides: a method for opening a seal comprising a metal foil and a layer of thermoplastic resin via which the seal is heat-sealed to the rim of a glass jar or equivalent container, said rim having been coated beforehand with a heat-sealing primer, the heat-sealed seal providing hermetic closure of the glass jar or equivalent container, characterized in that the initial and final tear forces are not more than 28 N on peeling of the seal at 90° at a speed of 300 mm/min; a glass jar or equivalent container suitable for implementation of this method, characterized in that the coating of heat-sealing primer comprises an organic and/or inorganic material in which organic and/or inorganic fillers are incorporated; and the application of this method or this glass jar or equivalent container to the packaging of processed food products.

Description

The present invention relates to glass packaging (jar, bottle with wide opening, bottle, carafe, ...) having a rim forming a surface of any geometry (annular, oval, substantially rectangular or other) and on which is heat sealed a metal seal providing a tight seal.

The rim is initially coated with a layer of heat-sealing primer, while the seal includes a layer of thermoplastic resin which allows heat-sealing by application of a sufficient temperature and pressure.

The problems that the user of this technique is confronted with are of several kinds.

It is of course essential to ensure a durable seal in the conditions of use of the packaged product, which may include temperature variations, or even biological transformations of the fermentation type ... The conservation of the product in compliance with the conditions prescribed for this effect must also be guaranteed.

The major problem posed by this technique lies in the often too great force to exert to open the package by peeling the lid. This too great strength can make the operation difficult for a young child or a relatively weak person. In addition, this difficulty of opening often causes tearing of the lid in several pieces, accompanied by residues of thermoplastic resin of the lid left in adhesion on the heat-sealing surface.

One could think to implement polymeric multilayer complex caps incorporating a cohesive rupture layer, but the heat sealing surface of the open package also has adhesive residues of thermoplastic resin originating from the lid.

The inventors therefore had the objective of solving these problems.

They have achieved this by the invention which relates to a method of opening a lid comprising a metal sheet and a thermoplastic resin layer through which the lid is heat-sealed on the rim of a pot or equivalent container of glass, having previously coated with a heat-sealing primer, the heat-sealed lid providing a tight closure of the pot or equivalent container of glass; this process is distinguished by the fact that the initial and final tearing forces are at most 30 N, when the lid is peeled at 90 ° at a speed of 300 mm / min, and that the primer heat-sealing comprises an organic and / or inorganic material in which mineral and / or organic fillers are incorporated.

Thus the opening of the package is easy even for a relatively small person, and avoids tearing the lid in several pieces during peeling. This easy opening is now achieved while meeting the sustainable sealing requirements required for all content, including food.

• les forces d'arrachement initiale et finale sont d'au plus 28, de préférence 25 N ;
• l'ouverture de l'opercule ne laisse aucun résidu de sa couche de résine thermoplastique sur le buvant du récipient en verre.

According to preferred features of the process of the invention:

• the initial and final tearing forces are at most 28, preferably 25 N;
• the opening of the lid leaves no residue of its thermoplastic resin layer on the rim of the glass container.

The subject of the invention is also an equivalent pot or container (bottle, flask, carafe, etc.) of glass suitable for carrying out the method described above, characterized in that the heat-sealing primer coating comprises a material organic and / or mineral in which are incorporated mineral and / or organic fillers.

In a particularly interesting embodiment, said organic material is the drying product of an aqueous dispersion of ethylene-acrylic acid copolymer whose carboxylic acid functions are partially or completely neutralized. This organic material may be alone or associated with at least one other organic and / or inorganic material - in addition to fillers - in the heat-sealing primer. This copolymer is solid and stable in its suspension at room temperature; the implementation by aqueous route is advantageous.

In addition, the pot coated with heat-sealing primer thus obtained can be delivered to its user-filler without delay, which eliminates the need to store more or less large volumes of pots before delivery.

The heat-sealing primer can contain mineral or organic fillers of one or more chemical natures, only mineral or organic fillers or both.

Preferably, said mineral fillers are incorporated in the dispersions of heat-sealing primer in the form of aggregates or powder of solid particles of sizes of between 1 nm and 20 μm, preferably between 150 nm and 10 μm, of one or more materials. selected from clays, kaolin, mica, talc, silicas, carbonates or alkaline earth sulfates, metal oxides.

When organic fillers are employed, they are advantageously of a different chemical nature from that of the heat-sealing primer (that is to say of the material constituting it excluding the fillers) as well as the thermoplastic resin of the cap, have a melting point higher than that of these two constituents and consist of particles of sizes of between 1 nm and 20 μm, preferably between 150 nm and 10 μm. Said organic fillers preferably comprise one or more polymers assembled in the form of copolymer, graft polymer, alloy or core-shell structure chosen from high density polyethylene (HDPE), polypropylene (PP), polystyrene (PS), polyamide (PA), polyester, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), poly (ethylene glycol) (PEG), polyethylene terephthalate (PET), polymethyl methacrylate (PMMA), polyetheretherketone (PEEK).

• au moins égale à 0,2, de préférence 0,9 et de manière particulièrement préférée 1,5 µm ;
• au plus égale à 4, de préférence 3 et de manière particulièrement préférée 2 µm.

The thickness of the primer coating of dry heat sealing on the rim of the glass container is advantageously

• at least 0.2, preferably 0.9, and particularly preferably 1.5 μm;
• at most equal to 4, preferably 3 and particularly preferably 2 microns.

Another object of the invention lies in the application of a method, or a pot or glass equivalent container described above, to the packaging of agri-food products, such as dairy or fruit-based, meat ( dough...). Indeed, the invention makes it possible to guarantee the preservation of the contents while respecting the conditions in particular of temperature prescribed for this purpose, and the tightness of the packaging in such conditions of conservation of the contents.

The invention is now illustrated by the following examples.

EXAMPLE 1 COMPARATIVE

• un pot en verre standard de type pot de yaourt ayant un diamètre extérieur de bague de 54,4 mm et une largeur de buvant de 4,2 mm, et
• un opercule composé d'une feuille d'aluminium de 47 µm d'épaisseur et d'une couche de résine thermoplastique déposée à 30 g/m², commercialisé par la société Alcan Packaging sous la référence Aluthène® 50 II E 114/2.

We use

• a standard yoghurt pot type glass pot having an outer ring diameter of 54.4 mm and a purge width of 4.2 mm, and
• a cover composed of an aluminum foil 47 μm thick and a layer of thermoplastic resin deposited at 30 g / m ² , sold by Alcan Packaging under the reference Aluthène® 50 II E 114/2.

A heat-sealing primer coating is deposited on the rim of the pot. Any other contact method, such as tempered, brush, buffer ... or without contact such as projection, spraying ... can be used.

Heat sealing the primary is organic and comprises an aqueous dispersion of random linear copolymer ethylene-acrylic acid of average molecular weight M _w of about 33 000 g / mol expressed in polystyrene equivalent. The copolymer comprises 9.1% of acrylic acid units and 90.9% of ethylene units. The carboxylic acid functions of the poly (ethylene-carboxylic acid) ionomer are neutralized to 100% with ammonia. The pH of the suspension is adjusted to between 8.5 and 9. According to the application method used, the solids content of the heat-sealing primer used varies from 0.2 to 10% by weight; it is here 9.5% in mass.

This material has a broad melting peak between 70 and 95 ° C (Differential Scanning Calorimetry - DSC - 15 ° C / min). The infrared profile of a dry extract of this material has a CH peak ratio (3020 - 2736 cm ^-1 ) on C = O (1772 - 1633 cm ^-1 ) of 3.2.

The heat sealing surface of the glass jar is roll coated with a uniform layer of primer having a mean dry thickness of 1.8 μm.

The heat sealing is carried out according to standard settings applied in industrial conditions, by means of a soft-head heat sealer delivering a thrust of approximately 1560 N. The head is heated to 250 ° C, so that the temperature at the interface pot / lid reaches 149 to 155 ° C for a duration of application of pressure by the heated head of 1.5 s.

The assembled system is waterproof.

The peel forces are peeled at 90 ° C at a speed of 300 mm / min. The typical known pattern of peeling on this type of system can be described in three forces: the initial tearing force (AI), the flow force (FE) and the final tearing force (AF).

• AI = 39 N
• FE = 26,2 N
• AF = 50,6 N.

The values given below are, as in the following examples, mean values over six pots:

• AI = 39 N
• FE = 26.2 N
• AF = 50.6 N.

The average of AI and AF is 44.8 N. The peeling of the operculum is therefore relatively difficult.

EXAMPLE 2

Example 1 is reproduced except that the heat-sealing primer is mixed with a suspension of Na ⁺ partition previously dispersed with the deflocculator in deionized water at a speed of between 500 and 1000 revolutions / min. 10 minutes. The solids in the mixture obtained are 9.5% by weight of primer and 0.6% by mass of Na ⁺ partition.

A homogeneous layer having a mean dry thickness of 1.8 μm is rolled.

• AI = 20,6 N
• FE = 10,5 N
• AF = 17,2 N.

We measure

• AI = 20.6 N
• FE = 10.5 N
• AF = 17.2 N.

The mean of AI and AF is 18.9 N, corresponding to a relatively easy operculum peel, the addition of Na ⁺ partitioning making it possible to reduce by more than 50% the force required for this purpose (to be compared with that of Comparative Example 1).

The operculum does not tear on peeling, after which no residue of thermoplastic resin originating from the lid is observed on the rim of the pot. The opening of the packaging can therefore be described as clean.

EXAMPLE 3

Example 1 is reproduced with the difference that the heat-sealing primer is mixed with magnetic stirring to an aqueous suspension at pH 8.5. of polytetrafluoroethylene (PTFE) whose particles have an average size of 155 nm and containing a surfactant which does not interfere with the adhesion to the glass. The solids in the mixture obtained are 9.5% by weight of primer and 4.5% by weight of PTFE.

Rolling is deposited a homogeneous coating of average dry thickness identical to that of the previous examples.

• AI = 26 N
• FE = 9,1 N
• AF = 24,6 N.

We measure

• AI = 26 N
• FE = 9.1 N
• AF = 24.6 N.

The average of AI and AF is 25.3 N, corresponding to a relatively easy operculum peel, the addition of PTFE making it possible to reduce by more than 40% the force required for this purpose.

The same remarks as in example 2 apply.

EXAMPLE 4

Example 1 is repeated with the difference that the thermosmoothing primer is mixed with magnetic stirring suspensions of Na ⁺ and PTFE partitions of Examples 2 and 3. The solids in the resulting mixture are adjusted to 9.5 % by weight of primer, 0.38% by mass of Na ⁺ partition and 3% by weight of PTFE.

The formulation is deposited according to the same process and the same thickness as the previous examples.

• AI = 13,5 N
• FE = 4,7 N
• AF = 16 N.

We measure

• AI = 13.5 N
• FE = 4.7 N
• AF = 16 N.

The mean of AI and AF is 14.8 N, corresponding to a very easy operculum peel, the joint addition of Na ⁺ and PTFE partitioning having allowed to reduce by more than 65% the force required for this purpose .

The same remarks as in example 2 apply.

Claims (11)

1. Method for opening a seal comprising a metal foil and a layer of thermoplastic resin via which the seal is heat-sealed to the rim of a glass jar or equivalent container, said rim having been coated beforehand with a heat-sealing primer, the heat-sealed seal providing hermetic closure of the glass jar or equivalent container, characterized in that the initial and final tear forces are not more than 30 N on peeling of the seal at 90° at a speed of 300 mm/min, and in that said heat-sealing primer comprises an organic and/or inorganic material in which organic and/or inorganic fillers are incorporated.
2. Method according to Claim 1, characterized in that the initial and final tear forces are not more than 28, preferably 25 N.
3. Method according to either of the preceding claims, characterized in that opening the seal does not leave any residue of said thermoplastic resin layer on said rim.
4. Glass jar or equivalent container suitable for implementation of a method according to any of the preceding claims, of which the rim is coated with a heat-sealing primer, characterized in that the coating of heat-sealing primer comprises an organic and/or inorganic material in which organic and/or inorganic fillers are incorporated.
5. Glass jar or equivalent container according to Claim 4, characterized in that said organic material is the product of drying an aqueous dispersion of ethylene-acrylic acid copolymer whose carboxylic acid functions are partly or totally neutralized.
6. Glass jar or equivalent container according to either of Claims 4 and 5, characterized in that said inorganic fillers are incorporated in the dispersions of heat-sealing primer in the form of aggregates or a powder of solid particles with sizes of between 1 nm and 20 µm, preferably between 150 nm and 10 µm, of one or more materials selected from clays, kaolin, mica, talc, silicas, carbonates or sulfates of alkaline earth metals, and metal oxides.
7. Glass jar or equivalent container according to any of Claims 4 to 6, characterized in that said organic fillers are chemically different from the heat-sealing primer and from the thermoplastic resin of the seal, have a melting temperature greater than that of these two constituents, and consist of particles with sizes of between 1 nm and 20 µm, preferably between 150 nm and 10 µm.
8. Glass jar or equivalent container according to Claim 7, characterized in that said organic fillers comprise one or more polymers assembled in the form of a copolymer, graft polymer, alloy or core-shell structure, selected from high-density polyethylene (HDPE), polypropylene (PP), polystyrene (PS), polyamide (PA), polyester, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), poly(ethylene glycol) (PEG), poly(ethylene terephthalate) (PET), polymethyl methacrylate (PMMA), and polyetheretherketone (PEEK).
9. Glass jar or equivalent container according to any of Claims 4 to 8, characterized in that the dry thickness of heat-sealing primer coating on the rim is at least 0.2, preferably 0.9, and more preferably 1.5 µm.
10. Glass jar or equivalent container according to any of Claims 4 to 9, characterized in that the dry thickness of heat-sealing primer coating on the rim is not more than 4, preferably 3, and more preferably 2 µm.
11. Application of a method according to any of Claims 1 to 3 or of a glass jar or equivalent container according to any of Claims 4 to 10 to the packaging of processed food products.