GB2125386A

GB2125386A - Closures for containers

Info

Publication number: GB2125386A
Application number: GB08321892A
Authority: GB
Inventors: Eugene Edward Davis
Original assignee: Johnsen and Jorgensen Ltd
Current assignee: Johnsen and Jorgensen Ltd
Priority date: 1982-08-17
Filing date: 1983-08-15
Publication date: 1984-03-07
Also published as: GB2125386B; GB8321892D0

Abstract

A container closure for carbonated drinks has a tamper- evident tear away feature and is made from a propylene-ethylene random copolymer in which the C3H6 and C2H4 monomers polymerise in random alternating sequence. The tear away feature is preferably an arcuate tear band 2 connected to the rest of the closure by a weakened membrane 12, 13 of a thickness in the range of 0.025 mm to 0.1 mm. <IMAGE>

Description

SPECIFICATION Improvements in or relating to closures for containers This invention relates to closures for containers of carbonated ("fizzy") drinks and to a carbonated bottled drink.

Conventionally carbonated drinks are sold in glass or plastic bottles with alternatives of metal crown closures, metal and plastic screw closures.

Such closures are quite satisfactory but we have been making experiments to see whether we can provide improved closure for use with carbonated drinks in which the closure is made of plastics material. In British Patent Specification No.1,387,556 there is disclosed a plastics crown closure made from a moulding composition of polypropylene and high pressure polyethylene. It is suggested that bottles sealed with such closures, containing drinks with a carbon dioxide content, remained perfectly tight on storage.

The present invention is concerned not with a crown closure, but with a plastics closure in which the closure incorporates a tamper evident feature as in our well known Jaycap. However we have encountered certain problems which may be summarized as follows:- 1. Closures of plastics material are usually made of polyethylene which is a strong and pliable material and which is capable of being torn especially if a line of weakness be provided as in the case of our Jaycap. However, although this closure is capable of holding air at high pressure, i.e. the closure forms a tight seal about the neck of the container, it has become apparent that polyethylene is permeable to CO2 and the pressure is dissapated at an unacceptable rate so that closures made of polyethylene are unsuitable for effervescent drinks pressurised with CO2.

2. Our experiments have shown that other plastics materials such as polypropylene which are not permeable by CO2 do not readily permit tearing so that the provision of a tamper evident feature incorporating a tear band is not possible.

We have continued our experiments for a number of years and while it has not yet proved possible to provide an impermeable polyethylene or practicable to treat the surface with an impermeable layer or coating, we have ascertained that the provision of a tearable plastics material based upon a plastics material in which propylene is the dominant monomer is possible. The types of materials which we have found most suitable are: (i) Material originally known under ICI Trade Mark Propathene grade PXC 2804 granules or 6804 powder and PXC 2907 granules or 6907 powder. These Propathenes are special medium and low flow copolymers, respectively, based upon the propylene monomer and PXC 2907 granules (now known as LSR 306) have been found to give the best results to date when moulded into container closures for carbonated drinks and including a tear-off band as a tamper evident feature.These Propathenes were specially designed by ICI to give unusual clarity and strength for the production of blow moulded bottles and containers and it is a complete surprise that these products incorporate a combination of the two necessary features i.e.

they are: 1. impermeable to CO2, and 2. tearable.

Moreover we would never expect to be able to injection mould a product with a blow-moulding grade of plastics where the plastics material, in order to support its own weight during the blowmoulding process must be of thick consistency or "toffeelike" and it was a complete surprise to us that this could be done.

(ii) Material similar to the ICI Propathene, being marketed by Shell in experimental quantities again for blow-moulding of bottles. They describe this material as random copolymer of propylene and ethylene and have designated the codes RMT 6100, PLZ 617, PLZ 624 to the relevant grades.

Random copolymers form products in their own right and can be placed in between polypropylene homopolymers and conventional polypropylene (block) copolymers.

The special structure of random copolymers, in which the propylene blocks are randomly interrupted by ethylene units gives them their unique properties. The impact strength is considerably better than homopolymer and, at equal ethylene concentrations, can be even higher than that of conventional copolymer. The randomly built-in ethylene units give the polymer a high degree of flexibility, which is not shown by other (conventional) polypropylenes. These two characteristics make random copolymers eminently suitable for applications such as squeezable bottles.

(iii) Material produced by Ato Chimie under their coding 3020/SN3 and (iv) Lacqtene P, a range of polypropylene and propylene-ethylene copolymers marketed by Ato Chimie. We have found to date that this product gives the best results for tearing and flexibility/elasticity properties. Moreover, it has a very low level of catalytic residues.

The common denominator in the aforementioned products is that the materials in question are propylene-ethylene random copolymers, in which the C3H6 and C2H4 monomers polymerise in randomly alternating sequence. The special grades are designed for blow-moulding yet, when subject to injection moulding which in itself if unexpected, surprisingly produce a product which is not only permeable to CO2 but tearable.

According to the present invention therefore we provide a container closure especially for use with carbonated drinks including a tamper evident tear away feature wherein the closure is made from a copolymer based upon the propylene monomer which is impermeable by CO2 and which can be torn by manual manipulation.

The invention also includes an injection moulded container closure having a tearable tamper-evident feature wherein the closure is made from a propylene-ethylene random copolymer in which the C3H and C monomers 6 2 4 monomers polymerise in random alternating sequence. In conventional plastics closures of polyethylene including a tear away band connected to the rest of the closure by a weakened membrane the normal thickness of the tearable membrane is in the range 0.1 mm to 0.25 mm. If the tearable membrane is below that range the closure would collapse on being applied to a container. In a closure in accordance with the invention made from a propylene-ethylen'e random copolymer, if the tearable membrane is made in the conventional range it simply will not gear.

However, although we know that conventional closures would not withstand the pressure of application if the tearable membrane was made less than 0.1 mm, we made further experiments with the copolymer. We were surprised to find that a membrane as thin as 0.025 mm could be moulded with the copolymer which would withstand application pressure and that within the range 0.025 mm to 0.1 mm the membrane was tearable, the optimum thickness being 0.05 mm.The precise design of the closure forms no part of the present invention but it may be said that the closure must be adapted to seat suitably on the container with which it is to be associated, so as to close the container and it must incorporate some form of tear off band as e.g. in our Jaycap or Securitainer closures so that unauthorised removal of the tear off band gives evidence that the contents of the container may have been tampered with. If desired the cap part of the closure may be remoable and replaceable.

As an example of a closure to which the present invention may be applied reference is directed to the accompanying drawings which illustrate the closure disclosed in our prior U.K. Patent No.

1,529,795 in which: Figure 1 is a vertical cross-section of a closure and Figures 2 and 2a are side views from different directions. Although full details may be obtained from the specification of our aforementioned patent to which reference is directed, the closure briefly comprises a cap part 1, a tear band 2 and an anchor band 3. The cap part 1 has a depending plug 5 and various sealing beads 6, 7, 8 and 9.

The tear band 2 extends about 900 around the closure, that is 450 on each side of a thumb tab 11 and the tear band 2 is connected to the cap part 1 by a weakened membrane 12 and to the anchor band 3 by a weakened membrane 13. The weakened membranes 12, 12 of the closure of the present invention preferably have a thickness of about 0.05 mm as previously explained.

Whilst the material of the present invention is primarily designed for use with carbonated drinks, we have also found that closures made from the same material provides for improved sterilisation.

The normal material from which closures are made, namely polyethylene, cannot be steam sterilised as such, yet we have found by experiment that where sterilisation is required, e.g. as with out Securipour product, steam sterilisation is now possible.

Claims

1. A container closure especially for use with carbonated drinks including a tamper-evident tear away feature wherein the closure is made from a copolymer based upon the propylene monomer which is impermeable by CO2 and which can be torn by manual manipulation.

2. A container closure according to claim 1 wherein the tamper-evident gear away feature is connected to the rest of the closure by a tearable membrane having a thickness in the range of 0.025 mm to 0.1 mm.

3. A container closure according to claim 2 wherein the tearable membrane has a thickness of 0.05 mm.

4. An injection moulded container closure having a tearable tamper-evident feature wherein the closure is made from a propylene-ethylene random copolymer in which the C3H6 and C2H4 monomers polymerise in random alternating sequence.

5. A container closure according to any one of the preceding claims herein the copolymer is selected from one or a mixture of the materials set out in types (i) to (iv) herein.

6. A container closure according to claim 4 or 5 wherein the tamper-evident feature is connected to the remainder of the closure by a tearable membrane the thickness of which is within the range of 0.025 mm to 0.1 mm.

7. A container closure according to any one of the previous claims wherein the closure comprises a cap part, an anchor band, a tear band between the cap part and the anchor band, a hinge connecting the cap part to the anchor band, and a thumb tab diametrically opposite to the hinge, wherein the tear band extends around the closure on each side of thumb tab towards the hinge for a part only of the distance between the respective ends of the thumb tab and the hinge and is connected to the cap part and the anchor part by respective weakened membranes, and wherein the part of the closure between the tear band and the hinge at each side of the hinge is spanned by a weakened tear line, the weakened membranes and the weakened tear line being of a thickness in the range of 0.025 mm to 0.1 mm.

8. An assembiy of a container and a tamperevident closure of plastics material, wherein the container contains liquid and CO2 gas under pressure, and wherein the plastics material is a propylene ethylene random copolymer in which the C3H2 and C2H4 monomers polymerise in random alternating sequence.