CA1157620A - Method for the closure of glass containers using plastic coated metal foil - Google Patents

Abstract

Abstract of the Disclosure Process for sealing glass or ceramic containers with a metal foil, in particular an aluminium foil coated on the side facing the con-tainer with a layer of plastic which melts under the action of heat and pressure. The rim of the container to be sealed is coated immersing in a solution which may be a pure organic or aqueous organic solution of an alkyl-trialkoxy-silane, an alkyl-trichlor-silane, or a mixed alkyl-alkoxychlor-silane, the alkyl group of which contains as a substitute an amino, epoxy, vinyl, acryl or methacryl group or an organic solution of a monomeric or poly-meric titanic ester. The deposit is dried and the sealing foil sealed onto the rim in a conventional manner using the heated head of a sealing device.

Description

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.1 Method for the closure of glass containers using plastic coated metal foil . :

The invention relates to a method for the closure of containers made of glass or ceramic materials using a metal foil, in parti-;cular aluminium foil which has on the side facing the container a llayer o plastic which melts under the influence of heat and ¦pressure . I
~ ~ i The use of plastic coated metal foils, so called heat sealing ¦Ijfoils, for the closure of plastic cups or similar plastic contai-~pers is known. The heat sealing layer on the foil is laid on the ¦container rim, which is usually in the form of a flange, and mel-ted there under the effect of heat and pressure by means of a ~sealing device. By choosing the correct plastic and sealing condi-~tions both the heat sealing layer and the rim of the cup melt and ~'fuse to form a strong permanent seal which is also bacteria and ~water p~oof. If, using the same method, the known heat sealing ¦,foils are applied to containers made of glass or ceramic materials, a relatively strong connection is formed initially between the container rim and the heat sealing foil . However, water vapour and even a relatively small amount of heating impair this seal so that it no longer guarantees the exclusion of bacteria, and the foodstuff in the container is spoilt.

IIt is therefore an object of the invention to improve the process ;
mentioned at the start in such a way that the seal produced at the . . .

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rim of the container remains strong, water and bacterial proof also under the influence of elevated temperatures and contents which contain water. This object is solved by way of the invention in that a purely organic or water containing organic solution of a monomeric or polymeric titanic ester is deposited on the rim of the container, the deposit dried and then the sealing foil sealed on to the rim in a generally known manner using a hot sealing device.
The organic solvents used for the titanic esters is preferably a benzine.
The concentration of the solvent is of second-ary importance in terms of the method of the invention;
however, the concentrations of solutions used are preferably 0.5 - 50/O.
The above-mentioned solution is usefully deposited on the rim of the container by means of a roller. All other methods of deposition are also possible e.g. immersion, spraying, or brushing. The deposit is simply to be applied in such a manner that the area on the container where the seal is to be provided is at least wet by the solution. The drying may take place at normal room temperature, or with the help of forced air or additional heat.

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The process of the invention is suitable both for glass containers which have been tempered and those which have not. It has also been found that the process of the invention is effective together ' with the widest variety of coating materials, when using heat sea~
ling foils. The materials which come into consideration are in particular extrusion coatings of polyethlene and polyprophlene and their copolymerides, grafted polymerides and polymerides; also ~surlyn polyester and polyamide coatings as well as heat sealing ~i 'foils which contain adhesives based on PVC, PVCAC, acrylate, metha-;
',,'crylate, polyamide, polyester, epoxide or polyeurathane compounds which can be cross linked as isocyanate.

,It has been found particularly advantageous to carry oud the pro-cess of the invention with a sealing head which has a sealing sur-face made out o an elastic material. A silicone rubber, which has ~' been made thermally conductive, has been shown to be particularly suitable for this purpose. To achieve a sufficiently high sealing temperature, it can be useful to embed the heating element of the ~sealing head in the elastic material.
~ . , ,Examplified embodiments of sealing heads which are particularly,suitable for carrying the process of the invention are illustrated ,in the drawings attached. Fig. 1 shows a cross section of a disc ~shaped sealing heaa 1, with spaces 6 in which an electrical heating element 2 is situated and connected to the power source via connec-tion 3. In the lower side of the sealing head facing the heat ,sealing foil there is a circular groove 4 which holds a ring shaped .
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,strip 5 of silicone rubber which is thermally conductive.

Fig. 2 shows a section through a disc shaped sealing head in which .,the electrical heating element 2 is embedded in the strip 5 of 'thermally conductive silicone rubber. This heating element 2 is connected to the power sQurce at connection 3 ~ia wirin~ which is ~not shown here but which passes through the sealing head and the `elastic strip to the heating element'2.

.The following examples help to explain the invention in greater I !detail .

'EXample'l .

~p solution comprising 96. parts by weight acetone, 2 parts by weight ,~water and 2 parts by weight amino-proyl-tri-ethoxysilane was pre-pared and deposited as a thin film on the rim of 2 preserving con-'tainers made of tempered glass using rolls with an adsorbent layeron them. The film was dried in an oven for one minute at 160 C.
These and two other glasses which had not been pre-treated were then filled with water to a level about 2 cm below the rim, and fitted with.a 0.04 mm thick aluminium strip coated with a PE acrylic ,acid copolymer. Using a sealing machine with a head fitted with a thermally conductive silicone rubber sealing surface a seal was formed between the heat s.ea,ling foil and the container rim; this step was completed in S seconds at 240 C.

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A glass sealed in accordance with the process of the invention and a glass sealed in the conventional manner were then stored at room temperature with the hot sealing foil at the ~ottom. whereas the '~onventionally sealed glass showed signs of imperfect sealing after ,five days the glass sealed by the process of the invention was still perfectly sealed after six weeks.

I~he two other flasses were placed in an oven at 75 C with the heat `sealing foil uppermost. After only 4 minutes under these conditions ~the conventionally sealed foil showed signs of imperfect sealing;
ithe g~ass sealing by the process of the invention was still per-~ectly sealed even after 45 min.

Exam~le 2 ,A solution of ~8 parts by weLght benzine (boiling range 100 - 140C);
,and 2 parts by weight of the polymer butyl titanate was prepared and deposited by immersion on the rim of 2 preserving containers made !l , ~of non-tempered glass. The deposited layer was dried in an oven for ~1 min at 160 C. After cooling to room temperature, these and two ,other glasses which had not been pre-treated were filled with water and sealed as in example No 1. The glasses were then stored under the same conditions as in the first example. The conventionally sealed container showed imperfect sealing after only 5 days at room temperature and the conventionally sealed container the same be-haviour after only 4 min at 75 C. The corresponding containers sealed by the process of the invention were still perfectly sealed fter 6 weeks and 45 min resp.

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~L~L~r~6'~0 SUPPLEME~TARY DISC~$URE , i - ~ -This example illustrates the improvements obtained using a titanate.
EXAMPLE III
The adhesive properties of the coating materials were investigated further in another series of trials com-paring the sealing effect using silanes with the sealing effect using titanates in accordance with the present invention, These trials involved the use of yogurt glasses of 150 cc capacity having at the mouth an outer diameter of 56 mm and an inner diameter of 50 mm, i.e., allowing a 3 mm wide surface at the rim for sealing on the foil. One series of such containers was coated at the mouth with a solution of ~-amino-propyl-tri-ethoxysilane and another series with a solution of polymerized butyl titanate. The deposited solution was then dried in an oven for 1 minute at 160C.
Glass containers so prepared were filled, some with water at a pH of 7, others with water at a pH of 1 (acidified with hydrochloric acid), and others with yogurt, then hot sealed with aluminum foil coated with a polyethylene-acrylic acid copolymer. The sealed glass containers were then stored in an autoclave at 40C and 80C.
The force required to tear off the sealing foil from the mouth of the container was then measured to deter-mine the force of adhesion of the foil both in the original state, i.e., on glass containers which had not been heated (reference value) and on those which had been stored at temperature for various durations, The measured values are shown in Table I, with the higher the numerical value the stronger the seal. In some cases the seal was not suffi-ciently tight to obtain a numerical value. The values given G

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are the average values from three measurements. On judging the results it should be noted that the width of the sealed region can vary somewhat due to lack of accuracy during the manufacture of the glasses, this causes the measured values to vary a little. Despite the foregoing, the measured values listed in Table I show that considerably better results were obtained with butyl titanate in accordace with the present invention than with silane.
Table I compares properties with no storage (reference value), stored at 40C for various times, and stored at 80C for two reference times. Peeling test measure-ments were conducted showing the starting force, i.e., the force necessary to commence peeling, and the propagation force, i.e., the force necessary to continue peeling. ;
Measurements were made after storing for 8 hours at 40C, It can be seen that none of the glasses with silane coating was still tight after this interval. Following this, a further test was made with silane pre-treated glasses filled with water pH 7 for 2 hours at 40C. Already after this shorter storage time a notable reduction in strength of adhesion could be observed.
Furthermore, it can be seen that the separation on the butyl titanate treated glasses took place between the adhesive and the coated metal foil and that the material around the opening remained intact even after the 80C and

2 and one-half hour test. On the other hand, with the silane pre-treatment, the separation on the stored glasses took place between the adhesive and the glass, and this around the whole of the opening periphery on the glasses which had been stored at 40C for 8 or more hours, or 80C and three-quarters of an hour or more, In the case of the glass ~576ZO

~ontainers which had not been stored or those held for 2 hours at 40C, the separation took place between the adhesive and the glass along about half of the peripheral region and between the adhesive and the coated metal foil over the other half. These observations also show that the butyl titanate pre-treatment allows remarkably better ad-hesion at the rim of a glass container than does a silane pre-treatment.

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~3 3 0 ~ 0 0 ~ ~ 0 ~ ~0 ~ ~o ~ 3 _ _ O 'O ~1 11~7~20 This invention may be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency are intended to be embraced therein,

Claims (10)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A process for sealing containers made of glass or ceramic materials with a metal foil which is provided on the side facing the container with a layer of plastic which melts under the action of heat and pressure, which comprises depositing on the rim of the container an organic solution of a monomeric or polymeric titanate ester, drying the deposit, and then sealing the foil on to the container rim using a heated head of a sealing device.

2. A process according to claim 1 wherein an elastic material is provided as the sealing surface of the head used to press the sealing foil on to the rim of the container.

3. A process according to claim 1 wherein said foil is aluminum foil.

4. A process according to claim 1 wherein an organic solvent is used for the titanate ester.

5. A process according to claim 4 wherein said solvent is a petroleum fraction with a boiling range from 100-140°C.

6. A process according to claim 2 wherein said elastic material is a silicone rubber which has been made thermally conductive.

7. A process according to claim 2 wherein the heating element of the sealing head is embedded in the elastic material.

8. A process according to claim 1 wherein the titanate ester is butyl titanate.

9. A process according to claim 1 wherein the sealing foil is an aluminum foil coated with a polyethylene-acrylic acid copolymer.

10. In a glass or ceramic container wherein the rim of said container is sealed with a metal foil which is provided on the side facing the container with a layer of plastic which melts under the action of heat and pressure, the improvement which comprises an intermediate adhesion pro-moting layer between said rim and plastic of an organic solution of a monomeric or polymeric titanate ester.