GB2087866A

GB2087866A - Sealing of aluminium foil membranes to glass containers

Info

Publication number: GB2087866A
Application number: GB8134900A
Authority: GB
Original assignee: United Glass Ltd
Current assignee: OI Glass Ltd
Priority date: 1980-11-20
Filing date: 1981-11-19
Publication date: 1982-06-03
Also published as: GB2087866B

Abstract

Problems arising from the packaging of aqueous products in glass containers heat-sealed by resin- coated metal, e.g. aluminium, foil membranes are alleviated by providing a glass sealing surface having a degree of hydrophobicity such that the contact angle of a drop of water on the sealing surface is in excess of 40 DEG . Methods involving the provision of a tin oxide coating on the glass, optionally with a subsequent long chain fatty acid and also possibly a polyolefine treatment, are described.

Description

SPECIFICATION Sealing of aluminium foil membranes to glass containers This invention relates to the sealing of containers by attaching to the sealing surface resin-coated aluminium foil membranes.

The sealing of aluminium foil membranes to glass containers is now a well established commercial process, and in our U.K. Patent Specification Nos: 1,135,943, 1,160,252, 1,207,306, 1,231,208, 1,289,298, 1,315,486/7 and 1,319,679 we have described methods by which such membranes may be sealed to glass and other containers by the application of an induction field, which causes the aluminium at the sealing edge to heat up and thus soften resin coated on the membranes and in contact with the container mouth. This method has proven highly satisfactory for the packaging of dry products, but where aqueous products have been packaged seal failure has occurred, in some cases after a relatively short period of time. This has, in the past, been attributed to attack on the glass by the water in the contained product, liberating alkali and contributing to the breakdown of the seal.

A number of methods have been proposed for overcoming this problem (e.g. as described in our U.K. Patent Specification 1,503,667), involving coating of the glass finish with a bonding agent, but this treatment poses a number of problems in terms of cost and effectiveness and has generally not been taken up commercially.

We have now found, in accordance with the invention, that effective and integral sealing of an aqueous product in a glass container by a resin-coated foil membrane can be obtained provided that the glass sealing surface is treated before the membrane is applied to provide a surface which is readily heat sealable to the membrane and has a degree of hydrophobicity such that the contact angle of a drop of water in contact with the surface is in excess of 40 .

Preferably the glass surface is treated in such a way that its water-resistant qualities are such as to maintain a contact angle in excess of 40 over as long a period of time as the seal is required to remain intact e.g. six to twelve months.

The glass containers may suitably be treated in the course of normal manufacture using suitable modifications of normal materials and techniques for surface treating the containers. Containers so treated are substantially free from problems in terms of toxicity or contamination of the contents of the container.

Glass containers may be provided with sealing surfaces having the specified hydrophobicity in a number of ways. (1) For example, the sealing surface may be treated, at a temperature in excess of 450"C, with a tin containing compound to provide a surface coating containing tin oxide, such that the tin content of the surface is in excess of 2 micrograms Sn per square cm. (2) Alternatively, the sealing surfaces may be treated at a temperature in excess of 450"C with a tin containing compound to provide a surface coating containing not less than 1 microgram Sn per square cm, the surfaces being subsequently treated at a temperature of 130-150 C with a polyolefine in suspension, followed by a treatment with a long chain fatty acid (e.g.C12 to C20) at a temperature greater than 75"C. (3) Again, the sealing surfaces may be treated at a temperature in excess of 450"C with a tin containing compound to provide a surface coating containing not less than 1 microgram Sn per square cm, the surfaces being subsequently treated at a temperature greater than 75"C with a long chain fatty acid. The treatments described above may take place immediately following the formation of the glass container, the tin oxide coating being applied prior to annealing the container, while the polyolefine and fatty acid treatments take place after annealing. The treatment prior to annealing takes place in a hood placed between the forming machine and the annealing lehr, while the treatments after annealing take place at the end or in an extension of the annealing lehr.The tin compound, polyolefine and fatty acid are respectively applied in spray or mist form. The retention of hydrophobicity is greatest for application (2), and least for application (1), but the energy required to effect a seal in the first place is least for application (1) and greatest for application (2).

Application (3) is intermediate in respect of both factors.

Such a technique will of course treat the entire external surfaces of the containers, as opposed to just the sealing surfaces, but this does not represent a disadvantage.

We have found, in a particular embodiment, that treatment of a glass sealing surface with a tin compound at a temperature of 500"C such as to provide a tin oxide coating on the surface with a tin content in excess of 1 microgram per square centimetre, followed by the application at a temperature of 90"C of oleic acid supplied as misted vapour, provides a surface which meets the hydrophobicity requirements set out above, while still allowing the resin-coated foil membrane to be sealed to the glass container under heating conditions used for normal foil membrane sealing of containers, for example those containing non-aqueous products.

1. A method of sealing an aqueous product in a glass container by a resin-coated metal foil membrane which comprises treating

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Sealing of aluminium foil membranes to glass containers This invention relates to the sealing of containers by attaching to the sealing surface resin-coated aluminium foil membranes. The sealing of aluminium foil membranes to glass containers is now a well established commercial process, and in our U.K. Patent Specification Nos: 1,135,943, 1,160,252, 1,207,306, 1,231,208, 1,289,298, 1,315,486/7 and 1,319,679 we have described methods by which such membranes may be sealed to glass and other containers by the application of an induction field, which causes the aluminium at the sealing edge to heat up and thus soften resin coated on the membranes and in contact with the container mouth. This method has proven highly satisfactory for the packaging of dry products, but where aqueous products have been packaged seal failure has occurred, in some cases after a relatively short period of time. This has, in the past, been attributed to attack on the glass by the water in the contained product, liberating alkali and contributing to the breakdown of the seal. A number of methods have been proposed for overcoming this problem (e.g. as described in our U.K. Patent Specification 1,503,667), involving coating of the glass finish with a bonding agent, but this treatment poses a number of problems in terms of cost and effectiveness and has generally not been taken up commercially. We have now found, in accordance with the invention, that effective and integral sealing of an aqueous product in a glass container by a resin-coated foil membrane can be obtained provided that the glass sealing surface is treated before the membrane is applied to provide a surface which is readily heat sealable to the membrane and has a degree of hydrophobicity such that the contact angle of a drop of water in contact with the surface is in excess of 40 . Preferably the glass surface is treated in such a way that its water-resistant qualities are such as to maintain a contact angle in excess of 40 over as long a period of time as the seal is required to remain intact e.g. six to twelve months. The glass containers may suitably be treated in the course of normal manufacture using suitable modifications of normal materials and techniques for surface treating the containers. Containers so treated are substantially free from problems in terms of toxicity or contamination of the contents of the container. Glass containers may be provided with sealing surfaces having the specified hydrophobicity in a number of ways. (1) For example, the sealing surface may be treated, at a temperature in excess of 450"C, with a tin containing compound to provide a surface coating containing tin oxide, such that the tin content of the surface is in excess of 2 micrograms Sn per square cm. (2) Alternatively, the sealing surfaces may be treated at a temperature in excess of 450"C with a tin containing compound to provide a surface coating containing not less than 1 microgram Sn per square cm, the surfaces being subsequently treated at a temperature of 130-150 C with a polyolefine in suspension, followed by a treatment with a long chain fatty acid (e.g.C12 to C20) at a temperature greater than 75"C. (3) Again, the sealing surfaces may be treated at a temperature in excess of 450"C with a tin containing compound to provide a surface coating containing not less than 1 microgram Sn per square cm, the surfaces being subsequently treated at a temperature greater than 75"C with a long chain fatty acid. The treatments described above may take place immediately following the formation of the glass container, the tin oxide coating being applied prior to annealing the container, while the polyolefine and fatty acid treatments take place after annealing. The treatment prior to annealing takes place in a hood placed between the forming machine and the annealing lehr, while the treatments after annealing take place at the end or in an extension of the annealing lehr.The tin compound, polyolefine and fatty acid are respectively applied in spray or mist form. The retention of hydrophobicity is greatest for application (2), and least for application (1), but the energy required to effect a seal in the first place is least for application (1) and greatest for application (2). Application (3) is intermediate in respect of both factors. Such a technique will of course treat the entire external surfaces of the containers, as opposed to just the sealing surfaces, but this does not represent a disadvantage. We have found, in a particular embodiment, that treatment of a glass sealing surface with a tin compound at a temperature of 500"C such as to provide a tin oxide coating on the surface with a tin content in excess of 1 microgram per square centimetre, followed by the application at a temperature of 90"C of oleic acid supplied as misted vapour, provides a surface which meets the hydrophobicity requirements set out above, while still allowing the resin-coated foil membrane to be sealed to the glass container under heating conditions used for normal foil membrane sealing of containers, for example those containing non-aqueous products. CLAIMS

1. A method of sealing an aqueous product in a glass container by a resin-coated metal foil membrane which comprises treating the glass sealing surface, before the membrane is applied, to provide a surface which is readily heat sealable to the membrane and has a degree of hydrophobicity such that the contact angle of a drop of water in contact with the surface is in excess of 40 .

2. A method as claimed in claim 1 wherein the glass sealing surface is treated, at a temperature in excess of 450"C, with a tin containing compound to provide a surface coating containing tin oxide in which the tin content is in excess of 2 micrograms of tin per square centimetre.

3. A method as claimed in claim 1 comprising treating the glass sealing surface, at a temperature in excess of 450"C, with a tin containing compound to provide a surface coating containing not less than 1 microgram of tin per square centimetre, subsequently treating the surface, at a temperature of 130-150"C, with a polyolefine in suspension, and then treating the surface at a temperature greater than 75"C, with a long chain fatty acid.

4. A method as claimed in claim 1 comprising treating the surface, at a temperature in excess of 450"C, with a tin containing compound to provide a surface coating containing not less than 1 microgram of tin per square centimetre, and subsequently treating the surface, at a temperature greater than 75"C, with a long chain fatty acid.

5. A method as claimed in any of claims 1 to 4 in which the respective treating materials are applied to the glass surface in spray or mist form.

6. A method as claimed in claim 4 comprising treating the glass surface with a tin compound at a temperature of 500"C to provide a tin oxide surface coating containing in excess of 1 microgram of tin per square centimetre, and then applying to the glass surface, at a temperature of 90"C, oleic acid in the form of misted vapour.

7. A glass container sealed by a resincoated metal foil membrane, and having a glass sealing surface produced by the method of any preceding claim.