Closures For Containers

Abstract

A screw-threaded metal closure for holding products, such as carbonated beverages, under pressure and of the type which is deformed at the top end of its cylindrical skirt during application so as to form a seal with the side of the bottle neck is provided with an upper row of outwardly pressed knurling and a lower row of knurling on an outwardly turned bead at the bottom margin of the skirt to enable a firm manual grasp to be obtained on a closure shell which has an exceptionally small skirt for economy reasons.

Description

The present invention relates to closures for containers for liquids and in particular containers for carbonated beverages, including beer, and to combinations of closures and containers for such purpose.

For many years it has been general practice to pack beer and other carbonated beverages in bottles which are sealed by means of the so-called crown closure. The crown closure is commonly made of tin-plate and its fluted skirt is engaged under a peripheral rib which extends around the neck of the bottle in close proximity to its mouth.

The crown closure suffers from two defects, namely that it requires a special tool to remove it from the bottle and that it cannot be used to reclose the bottle. However, it is extremely cheap to manufacture and moreover the bottles are commonly reused, so that it has not heretofore been practicable to replace the crown closure with a different type of closure since this has meant simultaneously discarding the user's whole inventory of bottles.

In recent years, however, non-returnable bottles have come into more general use and these have been adopted for some carbonated beverages. When non-returnable bottles are adopted it is practicable to adopt the most convenient form of closure consistent with economy in price. The most widely employed form of non-returnable bottle system for carbonated beverages has employed a bottle with an externally screw-threaded neck, having a cylindrical sealing surface between the top of the bottle and the start of the thread. With this bottle has been employed a closure in the form of an aluminum shell having a gasket covering the inner surface of the top of the shell and forming a thicker annulus in the angle between the top and the skirt of the shell, the gasket being formed by spinning or moulding a mass of flowed-in material.

The diameter of the skirt of the closure shell is sufficiently large to fit over the thread on the bottle neck at the maximum size allowed by the range of tolerances set out in the specification of the neck finish of the bottle. The skirt of this shell is deformed by a thread-rolling operation carried out in known way to bring it into engagement with the thread on the bottle neck.

In the first stage of applying it to the bottle, the closure shell is subjected to vertical pressure to press it down firmly against the top of the bottle. Although the thickened annulus of the gasket material makes an initial contact with the radiused surface joining the top sealing surface with the cylindrical side sealing surface on the bottle, the seal is improved by reducing the diameter of the top end of the skirt so as to squeeze the gasket material between the skirt and the cylindrical sealing surface on the bottle neck, thus increasing the vertical extent of the contact of the gasket material with the glass and also compensating for any ovality of the glass. This reduction of diameter is effected by a cylindrical throat which engages the periphery of the top of the shell and reforms it together with the upper end of the closure skirt. This reduction in diameter is however confined to a very short length of the upper end of the skirt and does not extend down as far as the row of inwardly pressed knurling provided for the gripping of the closure shell.

This known arrangement has been found sufficient to retain a pressure of about 12 atmospheres in the case of a bottle having a neck with an external diameter of 28 mms and is thus fully comparable in pressure-holding capacity with a crown closure. It is however hampered in gaining wider acceptance by the fact that it is substantially more expensive than the crown closure by reason of the greater cost of aluminium sheet as compared with tinplate.

It is the object of the present invention to provide a container system which is more nearly competitive in price with the use of crown closures.

In designing an improved container system of the present type two requisites must be borne in mind, firstly that the closure must have adequate pressure-holding characteristics and secondly that the closure must be capable of being unscrewed by the human hand and for this second requirement it must present adequate purchase for gripping between thumb and fingers.

For reasons of economy the closure shell must be made from the smallest possible disc and for this purpose the overall length of the skirt must be made as small as possible consistent with satisfying the conditions set forth above.

In order to keep the skirt of the closure as short as possible, it is also necessary to maintain the distance between the top of the bottle and the start of the thread as small as is consistent with forming a seal between the closure and the bottle. Any knurling, as is essential for grasping the closure, must be contained in the area of the skirt above the thread. However, when the vertical extent of the knurling in this area is small, it is found insufficient for applying sufficient torque by thumb and fingers to open the closure against the resistance characteristically experienced and according to a special feature of the present invention a second band of knurling is formed on an outwardly curled bead at the bottom margin of the skirt. This leaves the entire length of the skirt between the upper band of knurling and the bead free for application of thread.

According to another feature of the invention the upper band of knurling is formed by rolling the wall of the shell with a knurling roller from inside so that the ridges of the knurling project outwardly and do not decrease the thickness of the layer of the gasket material deposited in the shell. In this way the diameter around the knurl of the upper band is nearly approximated with the knurled bead at the bottom of the skirt.

According to one aspect of the invention a closure blank for application to a screw-threaded bottle by a thread rolling operation comprises a cup-shaped metal shell having a top and a skirt, a layer of gasket material covering the inner surface of the top and bonded thereto, said layer forming a thickened annulus in the angle between the top and the skirt, a band of outwardly pressed or embossed knurling being formed at the top end of the skirt, the skirt having an outwardly curled bead at its bottom margin, said bead also being knurled.

In addition to the formation of a pressure-holding seal between the shell and the bottle by means of the gasket material, the thread rolled into the skirt of the shell must be sufficiently strong to hold the closure onto the bottle. If the thread is not sufficient, the closure may be blown off the bottle by the internal pressure before leakage between the gasket and the bottle takes place. It has now been found that by decreasing the thread pitch a closure with a very short skirt may be secured to the bottle to withstand the force exerted by a pressure of 12 atmospheres.

In one arrangement made in accordance with the present invention the closure was of the 26 mm type; that is to say the closure had a diameter of 26 mms approximately. In this case the vertical distance of the sealing surface from the start of thread to the top of the bottle was set at 0.075 inch - 0.090 inch (1.91 - 2.28 mms), whilst the vertical extent of the thread on the bottle neck was set at 0.3 inches (7.62 mms), the thread being of conventional size and shape, except that the pitch was 8 threads to the inch (corresponding to a thread helix angle of 2.degree.23').

The blank of the closure for this bottle was produced from aluminium "container sheet" of a thickness of 0.0085 inch (0.21 mm) and had an initial diameter of 1.710 inches (43.43 mms).

Referring now to the accompanying drawings:

FIG. 1 shows the above exemplified closure blank, partly in section,

FIG. 2 is a part section of the closure blank of FIG. 1 after application to a bottle, shown in conjunction with a tool by which it is reformed on a bottle.

The closure blank illustrated in FIG. 1 comprises a top 1, a skirt 2 and an outwardly curled bead 3, which is knurled. A layer of gasket material 4 covers the top 1 and forms a thickened annulus 5 on the inside of the radiused corner 6 between the top 1 and the skirt 2. The weight of gasket material is approximately 350 mgms and it may be formed into the desired shape from deposited, viscous material by spinning and subsequent curing or by moulding in situ.

The height of the shell from the top 1 to the bottom of the bead 3 approximates to the distance from the top surface of the bottle to the bottom of its thread. A very narrow outwardly pressed band of knurling 7 having a vertical extent of 0.08 inch (2 mms) is arranged immediately below the radiused corner 6 and a shallow depression 8 lies at the bottom margin of the knurling 7. The top margin of the knurling 7 is at a distance of only 0.04 inch (1 mm) below the top 1, this distance being virtually the same as the radius of the corner 6 between the top 1 and skirt 2.

The closure is applied to the bottle by means of the tool set illustrated in FIG. 2, which is of the same type as illustrated in our British Pat. No. 975,739. In this operation the radiused corner portion 6 is reformed by the tool to a reduced diameter portion 6' and its external diameter is reduced to 0.975 inch (23.8 mms) from an initial value of 1.017 inches (25.8 mms). This has the effect of flowing the gasket material of the annulus 5 in the cylindrical space between the reformed radiused portion 6' and the corresponding cylindrical sealing surface 11 on the bottle, the diameter of which is 0.916 .+-. 0.010 inch (23.25 .+-. 0.25 mms). At the same time the plain portion of the skirt 2 below depression 8 is brought into engagement with the bottle thread 12 by a rolling operation in conventional manner.

Although the overall height of the closure on the bottle is only about 0.4 inch, it is found that it will retain a pressure of about 10-12 atmospheres. At the same time the upper and lower knurling at 7 and 3 allow the closure to be adequately grasped for unscrewing and to permit it to be unscrewed by a human hand of normal strength, providing that steps are taken during the bottle-filling process to maintain adequate cleanliness of the bottle threads.

Since the upper knurling is outwardly pressed the thickness of the gasket annulus 5 is not reduced by the individual ribs of the knurling 7 and as a result no difficulty arises in the event that the reforming throat of the tool slightly overruns the top end of the knurling in forming the reduced diameter portion 6'.

The reforming of the rounded corner portion 6 is effected in two consecutive movements. In the first movement the pressure block 19 descends onto the top of the closure and presses it firmly down against the mouth of the bottle so as to cause substantial deformation of the resilient gasket and in the second stage a throat member 21 descends to engage the peripheral portion of the top 1 by means of the rounded shoulder 22, which reforms the rounded corner portion 6 into the reduced diameter portion 6', which has an external diameter determined by the internal diameter of the throat member 21. While the closure is held in the position illustrated in FIG. 2, thread is rolled in the skirt by conventional thread rollers (not shown) operating in the conventional manner.

Claims

I claim:

1. A closure blank for application to a screw-threaded bottle by a thread rolling operation wherein the bottle has a cylindrical seal surface above the threads, said blank comprising a single piece cup-shaped metal shell having a top and a skirt, joined together at and continuous with a radiused corner, formed with an outwardly directed bead at its lower margin; and a layer of gasket material bonded to the inner surface of the top and extending around said radiused corner to form an annular seal the invention comprising said shell being formed with an upper band of outwardly pressed knurling at the upper margin of the skirt adjacent said radiused corner radially outwardly of and overlapping at least in part said annular seal and a lower band of knurling in said bead, said outwardly pressed knurling having outwardly extending ribs and the metal therebetween having a diameter approximating that of the lower portion of said skirt the positioning of said annular seal radially inwardly of said outwardly pressed knurling and the knurling on the lower bead permitting material economy by permitting minimum overall closure height consistant with forming a side seal between said gasket material and the cylindrical sealing surface of the bottle while also providing sufficient purchase to allow removal of said closure from the bottle by hand.

2. A closure blank according to claim 1 further characterised in that the upper band of knurling extends up to the radiused corner joining the top to the skirt.

3. A closure blank according to claim 1 further characterised in that the vertical extent of the upper band of knurling is about 2 mms.

4. The combination of a closure thread rolled on a bottle which has an externally threaded neck and a cylindrical sealing surface above the upper limit of the thread and the mouth of the bottle, the closure cap comprising a single piece metal shell having a top and a skirt joined at a radiused corner with an outwardly turned bead at its lower margin; and a layer of gasket material bonded to the inner surface of said shell at least extending around said radiused corner and on the adjoining cylindrical skirt, the invention comprising the closure skirt having a reduced diameter portion lying outwardly of said cylindrical sealing surface radially compressing said gasket material against said sealing surface to form an annular seal, a threaded portion lying immediately above said bead and a narrow upper band of outwardly pressed knurling lying radially outwardly of and overlapping at least in part said annular seal of gasket material between said threaded portion and said reduced diameter portion, the positioning of said annular seal radially inwardly of said outwardly pressed knurling and the knurling on the lower bead permitting material economy by permitting minimum overall closure height consistent with forming a side seal between said gasket material and the cylindrical sealing surface of the bottle while also providing sufficient purchase to allow removal of said closure from the bottle by hand.