GB2147288A - After treatment glass containers - Google Patents

Abstract

In a process for treating glass containers, e.g. glass bottles and jars, in order to enhance their subsequent sealing by coated aluminium foil membranes, the containers are treated, at the hot-end, with a metal-containing compound to produce a metal oxide, e.g. a tin oxide or titanium oxide, surface coating, followed by spraying with an ethylene/acrylic acid copolymer and a cold-end treatment with oleic acid.

Description

SPECIFICATION Manufacture of glass containers This invention relates to the manufacture of glass containers, e.g. glass bottles and jars, and is especially concerned with the production of glass containers which have a lubricous and abrasionresistant surface together with the ability to be sealed by means of a coated aluminium foil membrane by the action of heat applied to the periphery of the membrane where it is in contact with the rim of the container.

In the production of glass containers it is usual to treat the containers at the "hot end" and/or at the "cold end". The "hot end" treatment of containers normally involves treating the containers with a mist or spray of, for example, a tin or titanium-containing compound shortly after the containers are removed from the forming machine and whilst they are still at high temperature. This treatment provides a metal oxide coating of the glass surface, which enhances its abrasion resistance.

The containers then pass through the annealing lehr. They may be treated again, at the "cold end" of the annealing lehr, with, for example,a suspension of an olefin polymer to increase their lubricity.

During the past fifteen years or so it has been the practice to seal many containers with an aluminium foil membrane. This has involved placing an aluminium foil membrane, coated with a heatsoftenable material, for example a thermoplastics material such as "Surlyn", on the rim of the container, applying pressure to the membrane on the container rim, and heating the periphery of the membrane, for example by means of a radio frequency induction field, to soften the heat-softenable material and adhere the aluminium foil to the container rim.

Unfortunately it has been found that the surface treatment of containers at the "hot end" and "cold end" is not always compatible with the sealing of those containers by means of an aluminium foil membrane. The seals obtained are sometimes less than perfect. For this reason it has been proposed to treat the sealing rim of the containers, prior to sealing, to make them more compatible with the sealing process. For example, in our British Patent Application No:8134900 we have described a process for treating glass containers so as to render the treated surface sufficiently hydrophobic as to discourage migration of water along the glass surface of a filled container sealed with a coated aluminium oil membrane, since such water migration would subsequently undermine the efficiency of the seal.

However, there still remain problems. For example, while the bottles treated as described in our aforementioned Application were suitable for heat sealing many aqueous products, it has been observed that when certain food products, for example mayonnaise, are allowed to contaminate the glass rim prior to sealing, the degree of seal obtained is much less than that obtained with a clean glass rim. A further problem may arise in the sealing of wet or dry medicinal products where such products are stored for a considerable time, possibly under conditions of high humidity. For such products it may be necessary to ensure that the seal displays a positive indication that the pack has been opened, once it has been opened, and for this purpose it is necessary that removal of the foil should be accompanied by rupture of the foil material itself.Clearly this will be influenced to some extent by the thickness of the foil, but at "commercial" thickness of foil ranging from 9-50 micrometres it has hitherto been found impossible to ensure that such rupture takes place, since slow degradation of the seal bonding during storage results in a "clean peel" and if such a foil closure were to be replaced after opening it would not be obvious that the pack had in fact already been opened.

For economic reasons it is necessary that any process involving treatment of the sealing rim of the container before sealing does not involve an additional step in the production process.

The need exists therefore for a process for the manufacture of lubricous and abrasion-resistant glass containers which may be sealed by means of aluminium foil membranes without the necessity for the container rims to be specially treated prior to the sealing operation. It is the object of the present invention to provide such a process.

We have now found that if, in the process described in our Patent Application No:8134900, an aqueous suspension of a copolymer of ethylene and an acrylic acid, or a derivative of such copolymer, is sprayed onto the containers immediately prior to the containers being treated with oleic acid mist, then the containers produced, while still having sufficient lubricity and abrasion resistance to meet all requirements for handling, filling and transport, will permit heat-sealing by means of coated aluminium foil membranes, even in the presence of gross contamination by the product of the rims of the containers immediately prior to sealing.

The exceilent results achieved by the present invention may be enhanced if, when sealing takes place, the membrane is sealed not only to the top rim of the container but also to a portion of the side of the neck of a container immediately below the rim. In this respect, sealing in accordance with the technique described in our Patent Application No:8207922 is preferred.

In accordance with the invention the "hot end" treatment of the containers may involve any of those treatments at present used, for example the spraying on to the hot containers of a tin- or titanium-containing compound. In the "cold end" treatment, however, the containers are subjected, for example at a temperature between 120 and 135on, to spraying with an aqueous suspension of ethylene/acrylic acid copolymer, suitably stabilised with ammonia, followed by treatment with a mist of oleic acid. This combined treatment renders the container surfaces desirably lubricous, and adheres well to the heat-softenable coating of the coated aluminium foil membrane used for sealing.

The following examples are given to iliustrate the invention.

Example 1 (comparative) Glass bottles, immediatedly after forming and while still hot form forming, were treated with a solution prepared by reacting tin tetrachloride and n-butyl acetate, the liquid being applied to the bottles through four sprays, two on either side of a treatment tunnel straddling the conveyor wherein the bottles were transferred from the the forming machine to an annealing lehr. By adjustment of the throughput through each spray the amount of tin deposited on the bottle could be regulated and sufficient tin was applied to ensure that the bottles would subsequently possess adequate abrasion resistance.For this purpose the American Glass Research Hot End Coating Meter is commonly employed, and in this case a reading of at least 30 Coating Thickness Units was required, corresponding to approximately 3 micrograms of tin per square centimetre of glass surface. For measuring the tin deposited on the finish of the glass container the American Glass Research Finish Coating Meter was employed and in this case a reading of 10-15 Coating Thickness Units was required, corresponding to approximately 1 microgram of tin per square centimetre of surface.

Towards the end of the annealing schedule, the bottles, at a temperature of 100"C, were passed into a hood and were treated therein with a mist of oleic acid which was generated by atomising oleic acid into a heated chamber and allowing a mixture of vapourised oleic acid with air to contact the bottles. The oleic acid feed was maintained at around 0:3my per minute. The bottles were then cooled to room temperature. These bottles were divided into two groups. Both groups were filled with mayonnaise, but in the case of group 1 bottles every care was taken to ensure that no mayonnaise contacted the rim of the bottle, while with the bottles of group 2 the rim was contaminated deliberately with mayonnaise to such an extent as to cover between 50 and 100% of the rim area with mayonnaise.A Surlyn (Trade Mark)-coated aluminium foil membrane was placed on the top of each bottle and under the action of top load sealing was effected by maintaining the load while subjecting the membrane to an electric induction field. Over a wide range of top pressures and sealing times and energies, all of the group 1 bottles were found to seal satisfactorily, while none of the group 2 bottles effected a seal which lasted longer than a few minutes.

Example 2 A test was carried out as described in Example 1, except that after the bottles were annealed, but before treatment with oleic acid, and while at a temperature of approximately 1300C, they were sprayed with an aqueous suspension of a co-polymer of ethylene and acrylic acid, stabilised with ammonia (total solids 0.2% by weight). For this purpose a concentrated suspension of ethylene/ acrylic acid copolymer supplied by Dow as No. 483 was used and was diluted with de-ionised water in proportion 1 part of concentrate to 125 parts of water. This suspension was applied by means of an overhead spray which traversed the annealing lehr, the rate of spraying application being approximately 70mix per minute. The bottles were then passed into the hood for treatment with oleic acid as described in Example 1.Group 1 and group 2 bottles were tested as described in Example 1, and in this case satisfactory sealing was obtained not only with the group 1 bottles, but with all the group 2 bottles tested, a hermetic sealing life of several months being obtained.

Example 3 Bottles were prepared as described in Example 1 and in Example 2. Those prepared according to Example 1 were designated group A, and those according to Example 2 as group B. Both sets of bottles were filled with aspirin tablets, and sealed by induction heating with Surlyn-coated aluminium foil, the thickness of the foil being 9 micrometres.

The sealed containers were tested for efficacy of seal both immediately after sealing and after 3 months storage at a temperature of 409C and 95% humidity. In all cases, immediately after filling, it was not possible to remove the foil from the glass without tearing of the foil taking place, whereas in the samples tested after storage all of group A permitted removal of the foil from the container without tearing, a peeling action being obtained. The group B bottles, however, resisted such ready peeling, and it was found necessary to tear the foil in order to remove it from the container.

By means of the present invention it is possible to provide an indefinite seal for aqueous products; to form a seal on glass containers which have been surface-treated; to do this without the necessity for any special equipment, and therefore without any addition to manufacturing costs, to satisfy all medical, e.g. hygiene requirements; to seal through contaminated surfaces; to enable operation at high speeds; and, by suitable design of the foil membrane seal, to provide a tamper-evident closure if required.

Claims (5)

1. A process for treating a glass container comprising applying thereto, in a hot-end treatment, a metal-containing compound to provide a surface which has a coating containing a metal oxide and, in a cold-end treatment, spraying the container with an oleic acid mist, wherein immediately prior to the container being treated with oleic acid mist an aqueous suspension of a copolymer of ethylene and an acrylic acid, or a derivative of such copolymer, is sprayed onto the container.

2. A process as claimed in claim 1, in which the metal-containing compound applied in the hot-end treatment is a tin- or titanium-containing compound, producing a tin oxide or titanium oxide coating respectively.

3. A process as claimed in claim 1 or 2 wherein the ethylene/acrylic acid copolymer is stabilised with ammonia.

4. A process as claimed in claim 1, substantially as described in the Examples.

5. Glass containers treated in accordance with the process of any of claims 1 to 4.