CA1081657A

CA1081657A - Gaskets for container closures

Info

Publication number: CA1081657A
Application number: CA282,549A
Authority: CA
Inventors: James J.A. Davidson; Graham R. West
Original assignee: WR Grace and Co
Current assignee: WR Grace and Co
Priority date: 1976-07-13
Filing date: 1977-07-12
Publication date: 1980-07-15
Also published as: DE2731929A1; NL7707732A; FR2358356B2; FR2358356A2; IT1114633B; ES460667A1; GB1544684A

Abstract

Abstract of the Disclosure A method of closing a container with a "roll-on" type of screw threaded closure, comprises taking a closure blank with a moulded resilient gasket on the inner face of the end wall, the gasket being profiled so as to have a central circular panel and an adjoining annular bead which, when viewed in an axial cross-section through the closure, consists of a hump projecting above the level of the central panel of the gasket and terminating just short of the skirt of the closure, with the centre of area of the hump disposed closer to the skirt of the closure than is the centre of the base line of the hump. The closure and container neck are depressed axially to-gether to close the bottle-neck and to compress the hump-shaped bead of the closure axially and to deform the hump-shaped bead radially outwardly towards the skirt of the closure. The closure is reformed y diametral contraction of the root of the closure skirt above the threads of the container neck under "tight" reform conditions so that the bead of the gasket acts as at least a partial side seal against the upper part of the neck of the container. The closure skirt is then deformed radially inwardly against the threads of the bottle neck to for threads in the closure skirt corresponding to the threads on the container neck.

Description

108~6S~

This invention relates to sealing containers with gaskstted closures, in particular to the configuration (profile) of gaskets for threaded closures.
Container closures are provided with ga~kets primarily in order to prevent air from entering the container and/or los~ of contents of the container to the outside. Such gaskets are especially important in closures for containers which hold food or drink since contamination of the food or drink within a container by the entry of air before consumption can be a serious health hazard.
A major area of use of gasketted closures i~ for the closing of bottles, especially glass bottles.
In order to enable a customer to re-close the container after it has been opened it is desirable to provide a threaded closure which can be removed by unscrewing. One general type of threaded closure which has found widespread commercial acceptance with clo~ing of glass bottles is the in situ-threaded type in which threads are formed during or after the operation of closing the closure onto the threaded container neck. Generally, a closure which is initially unthreaded is closed by pressure onto the neck of a threaded container. Lateral pressure is then applied to impart threads to the skirt of the closure using the container neck as a die so that the threads formed in the closure correspond to those on the neck of the conta$ner. For example the threads may be formed with the aid of a roller. Closure caps having threads ; formed in this way are termed "roll-on" caps and are usually used on bottles.
Gaskets for closures of the above type have hitherto been produced by the so-called spin-line process. In the spin-line `~ - 2 - ~

: ' ' ' : ~ , , . ~
' 10816~7 process a predetermined quantity of a plastisol of polyvinyl chloride is metered into a closure, the closure is spun rapidly about an axis through the centre of the flat top of the closure so as to distribute the plastisol by the action of centrifugal force, and the plastisol in the closure is then fluxed. The plastisol is a viscous dispersion of polyvinyl chloride in a plasticiser and is fluxed by heating it to a temperature at which the plasticiser is absorbed by the polyvinyl chloride to form a homogeneous mass, which upon cooling gives a rubbery solid.
The spin-line process, although commercially succes~ful, has some limitations, and in our-R~ ~ l~cuL vrl Ne_ 17~1l6,'7~, we have proposed moulding certain gaskets which may ~; therefore have a profile different from those produced by the spin-line process. Before the closure is closed onto the container these gasket~, in their undeformed configuration, comprise a - substantially flat central panel and an adjoining peripheral portion, the thickness of which is at all points greater than the thickness of the central panel.
Looking at the closure (cap blank before thread formation) in its inverted or up-turned position, meaning the oppo~ite way up to which it is seen when closed onto a bottle, the peripheral portion of the gasket extends radially outwards to a point on the skirt of the closure which i~ overall upwards from the central panel of the gasket, and, considered in the radially outward direction, the height of the peripheral portion above the central panel starts by increasing and thereafter either continues to increaQe or remains the same.

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:: ' 108i~S7 United States Patent No. 3,255,909 discloses a linerless closure using an integrally moulded bead upstanding on the inner face of the closure end wall and adapted to fold radially outwardly to act as a top seal during closing of a bottle neck using such a closure. However top seal èffect alone is in~ufficient to ensure ade~uate ~helf life of ~assy liquid beverages such as soda water and other pressurised drinks.
In German Offenlegungsschrift No. 2,417,173 we described at Figures 11, 12 and 13, a moulded gasket profile in which the gasket had a central panel surrounded by an annular bead which stopped short of the closure skirt and was joined to the skirt by a foot portion of a height comparable to that of the central panel.
Such a gasket, after closing of the container and rolling of a thread on the container skirt using a "reform" operation gave a top seal which with a carefully formulated gasket composition would hold a venting pressure of as high as 100 p.s.i. In the "reform" operation, during the closing of the cap force is exerted not only downwardly but also laterally inwardly on the top of the skirt of the cap above the thread-forming zone of the skirt, so as to pinch the top of the skirt inward~. In other words, the diameter of the skirt is reduced \ 80 that, in the caqe of a spin-lined ga~ket profile as disclosed in B~itish Patent Specification No. 975,739, the gasket is compressed between the top of the skirt of the cap and the side of the neck of the ¢ontainer.
Although the said British Patent Specification No.975,739 did not ernphasise the degree of reform required, the reform operation widely employed commercially as a result of the invention claimed in . . .

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, :
, .

iOB~657 British Specification No. 975,739 has now been found to be capable of improvement by u~ing a more severe reform operation which will be referred to throughout thi~ Specification as "tight" reform.
The axial depth of the root of the closure skirt which is affected by the refonm is increased and the diametral contraction i^~ also increased so as to reduce still further the volume of the space remaining between the corner of the glass finish of the bottle neck and the corner of the closure.
One aspect of the pre~ent invention provide~ a method of closing a container with a "roll-on" type of screw threaded closure, such method comprising: taking a closure blank with a moulded re~ilient gasket on the inner face of the end wall of the closure, which gasket i8 profiled 80 as to have a central circular panel and an adjoining annular bead which, when viewed in an axial cross-section through the closure, consists of a hump.projecting above the level of the central panel of the ga~ket and terminating just short of the skirt of the closure, with the centre of area o~ the hump disposed closer to the skirt of the closure than is the centre of the base line of the hump7 pressing the closure and container neck axially together to close the bottle-neck and to compress the hump-shaped bead of the closure axially and to defonm the hump-shaped bead radially outwardly towards the skirt of the closure, reformlng the closure by diametral contraction of the root of the closure skirt above.the threads on the container neck under "tight" reform conditions 80 that the said bead of the gasket acts as at least a partial side seal again~t the upper part of the neck of the container, and deforming the closure skirt radially inwardly against the threads ~ 5 ~

: ,,, -.

1081~

of the bottle neck to form thread~ in the clo~ure ~kirt corresponding to the thread~ on the container neck.
By using tight reform condition~ with an annular-beaded ga~ket moulded to h preci~e profile, it i~ possible to reduce drastically the volume of ga~ketting material necessary to achieve both a top seal and a ~ide ~eal effect. Whereas the spin-lined form of closure proposed in Patent Specification No. 975,739 traditionally employs film volume~ of 400 mm3 or thereabouts in the ga~ket, judiciou~ selection of the gasket profile for use with the present invention enables a quite satisfactory sealing effect to be obtained with a gasket having a film volume of the order of 200 mm3.
In a preferred form of the first a~pect of the present invention the hump-shape o the cro~s-section through the gasket ~ead is in the form of a truncated triangle having its base parallel to the end wall of the closure, a ~ub~tantially straight radially inner side of the triangle being digposed at an angle of from 15 to 70 with respect to the plane of the closure end wall, and a substantially straight radially outwardly facing side being disposed at an angle of from 70 to 86 with respect to the plane of the end wall.
In one particularly convenient form of the pre~ent invention the radially inwardly facing side of the triangular hump i8 inclined at an angle of 54~ to the plane of the closure end wall, the radially outwardly facing side is inclined at an angle of 74 to the end wall, and the height of the hump above the general level of the central panel of the gasket i~ 1.07 mm with a flat truncated top to the triangle.

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lOB16S7 The invention also relates to bottles which have been closed by the method of the first aspect of the present invention.
Another aspect of the present invention provides a gasketted closure compri~ing a closure end wall having a generally cylindrical skirt depending from its periphery; and a gasket moulded on the inner face of the end wall of the closure with a gasket profile comprising a circular central panel bounded by an upstanding annular bead which bead is spaced from the skirt of the closure by a foot portion of the gasket having a height substantially the same as that of the central panel of the gasket, the profile of the bead being such that, in an axial cross-sectional view, the bead consists of a substantially triangular hump haviny its centre of area disposed closer to the skirt of the closure than is the centre of the base-line of the hump, with the radially inwardly facing substantially straight side of the triangular hump inclined at an angle of from 15 to 70 with respect to the end wall of the closure, the radially outwardly facing side of the triangular hump being substantially straight and inclined at an angle of from 70 to 86~ with respect to the said end wall of the closure, and the triangular hump having a truncated top. The truncated top is in the form of a radiused apex or a flat top face to the hump.
If desired, with the method or the closure of the present invention, the said central panel of the gasket may include a series of concentric annular ribs.
The hump constitutes the main part of the peripheral portion. It will usually have a height of 0.7 to 2.5 mm. above the central panel and the area of it will usually be in the range 0.9 to lOR16~7 3 . 7 9q . mm. Its radial length is much greater than that of the foot part.
The foot part typically ha~ a radial length of from 0.25 to 0.16 mm. and its thicknes~ is typically from 0.1 to 0.35 mm.
(mea~ured perpendicularly to the corner of the cap).
The marginal part correspond~ to the tolerance between a moulding member used to mould the gasket in the cap blank and the minimum diameter of the cap blank itself. It will generally have a radial length of about 0.02 to 0.15 mm~
The invention will be explained, and particular embodiments described, with reference to the accompanying drawings, in which:-Figures 1 to 3 are vertical ~ections, through part of a radius, of the corner of a gasXetted cap blank of the invention, showing the configuration of the peripheral portion of the gasket:
Figure 4 is a partial vertical section of a moulding member used to make the gasket of Figure 1 Figure S ~hows a side elevation of the glass bottle neck onto which the gasketted cap blanks of the invention can be closed, Figure 6 i~ a sectional view showing the profile of Figure 3 just prior to closing of a glass bottle neck, and Figure 7 i8 a sectional view showing the closurs corner and a gasket bead of a further embodiment of gasket.
Reference is directed first to Figure 1 to explain the invention generally. The cap blank 1 of internal diameter in the range from 25 to 32 mm., i8 preferably made of thin aluminium, typically of a thickness in the range from 0.20 to 0.30 mm., and will normally be lacquered on the inside and outside. The cap blank is ' . .

~hown in it~ up-turned position relative to that which it occupies on the container and compri~es a s~irt 2 upstanding from a ba~e 3.
The ga~ket, which i~ made of a re~ilient plastic~ material, has a flat central panel 4 and an adjoining peripneral portion designated generally at 5.
The peripheral portion of the ga~ket i~ bounded by the ~olid lines M, N, 0, P, Q, R. Taking it radially outwards from the edge M of the central panel 4, the hump portion 6 is bounded by M, N, 0 and P, the adjoining foot portion 7 lie~ beneath PQ
and the marginal portion 8 beneath QR.
To facilitate explanation of the dimension~ of the peripheral portion, Figure 1 include~ broken lines which are line~
of geometric construction as follows:-The hump portion 6 shown consi~ts of a slope of constantgradient extending upwardly from the edge M of the central panel and making an angle therewith. me top of the slope is denoted by N. In~tead of a 810pe of constant gradient, a convex or concave slope could be given to this part of the hump. The summit of the hump N0 may be flat as in Figure 1 or rounded as in Figure 3. At the point 0, a steep downward 810pe OP, conveniently but not necessarily, of constant gradient begins. In principle this downward slope could be vertical, but practical considerations of moulding dictate that the angle made by this slope with the plane of the central panel be normally in the range 75-86.
In order to form a sati~factory ~eal between the neck of the container and the cap, it is necessary to ensure that an adequate supply of gasket material i9 positioned in the corner part ' ~ , ' 1~816S7 of the cap blank. The present invention enables this supply to be provided without leaving flashing up the skirt to an undesirable extent in that the supply in the corner is provided by deformation of the hump 6 and foot portion 7 together with the deformation of the bottom of the skirt 2 under tight reform conditions. Thus the gasket moulding member (refer to Figure 4) has a hollowed-out portion 6a which provides the hump 6 of the gasket and an annular flange 7a which forms a leg when viewed in an axial cro~s-section, -extends down to about the level of, or slightly above, the central panel and thereby limits the extent to which gasket material can creep up the skirt during the moulding of the cap blank. '~he leg 7a of the mould cross-section corresponds to the foot part 7 of the gasket. The leg 7a may be cut away slightly upwardly and radially outwardly at its lower end, as in Figure 4, e.g. at an angle of 25 with the horizontal, so as to enable it to conform better to the curved corner of the cap blank. Thus the radially outward end Q of the foot part 7 of the gasket may be above the point P at which the foot part joins the downward slope of the hump. The foot part 7 may include a flat portion PS, as illu~trated in Figure 2, or be wholly flat, a~ illustrated in Figure 3.
The leg 7a of the moulding member must be given a certain minimum radial thickne~ in order to give it enough mechanical strength to withstand repeated use in high-speed moulding operations.
Of course this minimum radial thickness will depend on the toughnes~
of the particular metal used for the moulding member, but in general it will not be les~ than ~.25 mm. On the other hand, the leg 7a must not be made too thick in the radial direction, since otherwise _ 10 --, : ~ .

~0816S7 the hump will be located too far radially inwards, with the result that the supply of gasket material in the corner of the cap blank may be in~ufficient to form the corner ~eal even under tight reform condition~.
It will now be evident why tbe slop~ OP is steep:
it is important to provide as much gasket material a3 possible in the radially outward region of th~ hump, but it i~ also important to allow for a reasonable thicknes~ for the leg 7a o~ the moulding member, particularly at the root of the leg 7a. A ~teep slope enablea both requirements to be met, and al50 ensures that the radially inner face of the flange forming the leg can be withdrawn from the radially outwardly facing part o~ the an~ular profile hump during removal or "stripping" of the mould from the closure.
The volume of the hump, or the area o~ the hump in vertical section in Figure l, should be kept as small as po~sible in order to achieve maximum economy of gasket material consistent with obtaining a reasonable seal. The sectional area will typically be rom 0.5 to 3.7 sq.mm, but it may be possible to u9e even less ga~et material, and of course there i8 no upper limit other than that dictated by common Yense and economies. A rough guide to the area under the hump may be obtained from the constructed triangle KLM, in which K
i8 a conqtructed point representing the intersection of a line vertically through point 0 with an extrapolation o~ the upward slope MN and L is a point coplanar with the central panel and vertically beneath 0. The area of triang~e KLM is equal to B2cot where B i~ the distance KL. Usually the angle a will be between 15 and 70~.

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10~16S7 Construction lines have been drawn in Figure 1 to show the centre of area G of the triangle KhM, i.e. the point at which the medians of the triangle meet. Referring now to Figure 5, it is desirable that the point marked T on the glas~ neck, i.e. the point at which the flat top 10 ends and curvature 11 leading to the side-wall 12 begins, should impinge upon the gasket at a point vertically above the centre of area G or not greatly distant radially from G. The cap blank, gasket dimensionq and glass neck configuration should be arranged accordingly. When the closure ga~ket i9 pressed hard axially onto the glass finish of the bottle neck during the closing operation, and the root of the clo~ure skirt deformed radially inwardly upon tight reform of the closure, the gasket material is pushed around the corner of the glass finish so that a substantial proportion eventually lies between the skirt 2 of the cap blank and the curvature 11 and side-wall 12 of the finish.
It is considered most advantageous for the displaced gasket material to come into contact with the clo~ure skirt as a result of the reform operation.
It will be appreciated that there may be curvature in the region of points M, N, 0, P and Q to facilitate obtaining a good definition by moulding.
For ease of reference Figure 1 also shows lines of geometrical construction dependent perpendicularly from M, G, 0, P, Q and R onto the closure end wall at points U, V, W, X, Y and Z
respectively.
Figure 6 shows in more detail the cross-~ection of the gas~et of Figure 3 and illustrates the relative positioning of the ~: ' ' - . , ~ :' :' :

gasket and the radially outwardly rounded end of the glas~ neck of a bottle on which the closure i~ to be fastened by a "tight"
reform thread rolling operation.
Figure 7 ~hows an alternative form of the gasket with certain differences from the form shown in Figure 6, for example Figure 7 shows a flat top face to the truncated triangular section of the hump, making it in effect of trapezoidal section.
The following Table gives dimensions of the ga~ketted cap blanks of Figures 6 and 7. These gasket~ are in accordance with the invention and give a satisfactory ~ealing performance when closed as roll-on bottle cap~ onto a bottle nec~ by a tight refonm operation.

108~6S7 TABLE

Fig. 6 Fig. 7 . .
Internal diameter of cap blank 27.35 27.35 Radial tolerance of moulding member (ZY) O.025 O.025 .A
Radial distance tYX) 0~32 O.32 .
Height (KL) 1.128 1.265 . .
Vertical truncation distance(R0) .516 .198 - . . __ : ~adial distance (YW) ,460 .622 ., Height of P abovo çentral panel 0.127 0.127 .
Angle a 3054~o - ~ 2 .
Area of triangle KLM (=~ cota) 1.102 .571 8q~. 111111. 9q. ~ .
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- 14 _ ~- , , ' , ~08~6~7 Con~iderable variation is po~Rible from the dimen~ions given in the Table, but in general the overall volume of gasket material ("film volume") will be much les~ than the 400 cu. mm.
frequently needed for spin-lined gasket~ in thi~ type of cap. A
film volume as low a~ about 200 cu. mm. can ea~ily be attained by the pre~ent invention.
These gasket configuration~ have been found to be effective, when formed of ~la~tici~ed PvC or other suitable plastic material, under both tight and loose reform conditions, allowing in each case a reduction in the quantity of plastics composition used in the gasket.
The preferred method of closing the cap blank onto a container comprise~ placing the gasketted metal cap blank (which by definition i8 of course made of thin metal) over the threaded neck of the container, pressing the cap blank down axially against the neck of the container, and whilst holding it 80 pressed, reducing the diameter of the skirt of the cap blank at a position above the threads on the neck of the container, in this case near the root of the closurQ skirt, 80 as to compress the ga~ket material between ; the top of the skirt of the cap blank and the side of the neck of the container, and forming thread~ in the skirt of the closure by deforming it at a position and in a configuration corresponding to the threads on the neck of the container. The reform operation, which will normally just precede the operation of forming the threads, may be effected by use of a clo~ure head of suitable shape, as described in British Patent Specification No. 975,739.
However, although there was no particular significance attached in British Patent Specification No. 975,739 to the extent ~0816S7 of reform, the method of the pre~ent invention involves what i8 termed "tight" or "~evere" reform in which the severity of the reform operation is increased over that used in both Briti~h Patent Specification No. 975,739 and our said German Offenlegungsschrift No. 2,417,173. This reduce~ the amount of gasket material necessary compared with the volume neces~ary in the spin-line proces~.
In a "tight" or "severe" reforming operation, a 28 mm.
(external diameter) cap blank may have its external diameter reduced to about 26.3 mm., instead of the 26.5 mm. u~ual in reforming and the depth over which the cap blank is reformed i8 1.7 to 1.9 mm.
instead of the 1.6 to 1.7 mm., u~ual in loose reforming. In practice a typical 1003e reform die for u~e with a 28 mm. diameter cap blank ha~ a reforming reces~ 26.3 mm. in diameter and 1.9 mm. deep to give the above loose reform re~ults and a typical tight reform die ha~
its rece~s 2.4 mm. deep and 26.0 mm. in diameter. The mouth of the reforming reces~ in the die i~ of course tapered as shown in Figures 4 and 5 of Patent Specification No. 975,739. Thus under tight reform conditions on a 28 mm. cap blank the diametral reduction i5 6.07%
instead of 5.35% usual with loose reform.
The above de~cribed "tight" or "severe" reforming increases the tendency of the material in the corner of the gasket to suffer 108a of adhesion, and the ga~ket~ therefore have a configuration which act~ counter to thi~ tendency, in that the centre of area of the profile hump 6 is disposed radially outwardly beyond the centre of the ba~e of the hump (when viewed in axial cross-section) 80 as to enhance the tendency of the reform operation to cause the ga~ket . ' , ' ' -~0816g7 material in the radially outward region of the hump 6 to be squeezed towards the periphery of the cap. Thu~, wherea~ in previou~ly propo~ed moulded gasket~ there i~ a large amount of corner material present in the gasket of the cap blank, as for example in our said Offenlegungsschrift No. 2,417,173, in the present invention the amount of gasket material initially in the corner i~ reduced, but thi~ is compensated for by movement of material into the corner during the reform operation. Since relatively little material is present in the corner initially, the moment of the force which decreases adhe~ion iY relatively small.
The axial force exerted by the clo~ing head downwardly on the cap blank may vary widely, e.g. from 120 kg. upwards, normally from 180 to 22~ kg.
The gasketted cap blanks of the invention may be closed onto a variety of containers, but it is envisaged that the invention will be of use mainly for cap3 clo~able onto glass bottles. The glas~ bottle~ may have gla~ finishes ~necks) of various types. One well known type ~hown in Figure 5 i~ the so-called "MCA 1 finish", widely used in Germany, Belgium, Netherlands and Luxembourg. The locking band 13 located below threads 14 iq wider than on ~ome other fini~he~ 80 that the MCA 1 may, if desired, be used with a pilfer proof type of roll-on cap, i.e. a cap with a long ~kirt which become~
closed over the locking band 13 and into the area 15 of narrower diameter below it. The bottom or rim of the cap skirt i~ then preqsed into the container neck in the area 15. A narrow band which i9 easily frangible is provided in the skirt of the cap in the region corre~ponding to the locking band 13. It is then impo~ible to unscrew 10816~7 the cap from the neck without causing fracture at the said narrow band~ The diameter t of the threads in Figure 5 is typically 27.65 mm., the diameter e of the rim corre~pondingly 25.25 mm., and the height h from the rim of the nec~ to the top of the locking band about 9.65 mm.
I A series of comparative tests was carried out using profiles similar to that illustrated in Figure 6 but with variation9 in the angle a between the end wall of the closure blank and the radially inwardly facing side 21 of the triangular hump 22 of the gasket profile. The height A of the rounded apex 24 of the profile hump above the general plane of the top face 23 of the central panel 4 of the gasket was varied but the angle of the radially outwardly facing side 25 of the triangular profile hump with respect to the end wall of the gasket was maintained at 74. The height of the foot portion 26 above the general plane of the central panel 23 was maintained at 0.127 mm. throughout. The results showed that optimum venting pressure values in the sealed bottle could be obtained using a value for the angle a ~ 54~ and A ~ 0.042" ~1.07 mm.). In thi8 case the venting pressure was in excess of 120 lbs. per sq. inch as determined on a te~t rig using a glass bottle which had the bottom connected to a source of gas under pressure and wa8 placed under water while the different internal pressure9 were applied up to a test rig maximum ~for safety purpose9) of 120 p.s.i. to observe at what pressure value gas bubbles could be seen to be escaping from the bottle to indicate the onset of venting.
Satisfactory results were obtained with an angle a = 30 and dimension A= 0.035" (0.889 mm.) where the film volume was then ` i ~ ~ ' -- . : ':
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substantially 200 mm3. Thi~ represents a most economical form of closure gasket, particularly compared with the traditional film volumes of 400 mm3 or more when using spin-lined closure~.
With the tight reform conditions to which the metallic closure blank is subjected during the bottle closing operation, and a judicious choice of gasket composition and gasket profile, it is possible with the method of the present invention to clo~e a bottle using film volumes of the order of 150 to 200 mm3 to withstand a venting pressure of 120 p. 8 .i. or more and causing the triangular hump of the gasket bead to migrate radially outwardly to occupy the space between the radiused or toroidal surface portion 27 of the end of the bottle neck 28 and the corner of the closure cros~-~ection between the end wall 3 and the skirt 2. This achieves the highly desirable results of combined top seal and side seal effects using film volumes which are of the order of one half those previously considered nece~ary in order to achieve combined top and side seal effects.
Naturally, when selecting the values of the various parameters of the configuration of the gasket, the flatter form of gasket (i.e. when the dimension A is ~mall) will be more economical in film volume. However there is of cour~e a minimum depth of gasket bead for achieving the degired venting pre3sure values.
In the present invention the minimum value of film volume of gasket attainable has been lowered by combining a moulded gasket profile with combined top ~eal and side seal effects using a gasket bead which readily migrates outwardly during axial compression and "tight"

(and in many ca~es also "loo~e") reform. Thus, after clo~ing, the bead advantageously ends up in contact with the previously exposed part of the root of the clo~ure skirt.
The gaskets may be formed within the caps by moulding them, u~ing a punch (moulding member). A quantity of gasketting material i~ deposited within the up-turned cap which, when appropriate, may be pre-heated. It will normally be neces~ary to heat the gasketting material to Yoften it and help it to adhere to the surface of the cap. It i~ then moulded with the punch, which may optionally itself be heated. The methods of moulding well known to those skilled in the art of gasketting "crown" bottle cap~ have general applicability.

It is for example possible to mould the gasket~ by the CGn~ian two stage punching process de~cribed and claimed in our ~i~i~h ~ote~ J 0~3,060 ~atont ~pli6a~ion ~7O, '~00l~5f~3 uQing a hot preheating punch to partially form the pla~tics material and a relatively cooler final moulding punch.
In principle, any gasketting material may be employed in the pre~ent invention. Suitable materials include e.g.
polyethylene, a mixture 80% or more polyethylene with up to 20% of a compatible polymeric material, a mixture compri~ing polyethylene, butyl rubber, and optionally an ethylene/vinyl acetate copolymer, especially polyethylene h utyl rubber mixtureq containing e.g. 40-70%
by weight of polyethylene and 60-30% by weight of butyl rubber.
Gaskets are preferably formed from thege mixture~ by cold-moulding as described e.g. in our Briti~h Patent Specification No. 1,112,023, ~`t .~ . ~ - , - ' , .
, 108~6S7 Australian Patent Specification No. 420,653 and German Auslegeschrift 1,544,989. Other u~able gasketting material~
include plasticised polyvinyl chloride and other vinyl chloride polymers known in the gasket-making art, other materials described in our Briti~h Patent Specification~ Nos. 1,112,024 and 1,112,025 and thermoplastic block or part-block/part-random copolymers of butadiene with styrene, optionally in admixture with other materials ~uch a~ polyethylene. This cla~s of material~ is dascribed in our British Patent Specifications Nos. 1,196,125 and 1,196,127.
The gasketting materials may of cour~e contain any of the usual additive~ such a~ a stabiliser, plasticiser, pisment, dye, filler, 91ip agent or lubricant.
The invention includes containers, especially bottle~
filled with beverage~ for human con~umption, closed by the proces~
of the invention.

Claims

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

1. A method of closing a container with a "roll-on" type of screw threaded closure, such method comprising (a) taking a closure blank with a moulded resilient gasket on the inner face of the end wall of the closure, said gasket being profiled so as to have a central circular panel and an adjoining annular bead which, when viewed in an axial cross-section through the closure, consists of a hump projecting above the level of the central panel of the gasket and terminating just short of the skirt of the closure, with the centre of area of the hump disposed closer to the skirt of the closure than is the centre of the base line of the hump;
(b) depressing the closure and container neck axially together to close the bottle-neck and to compress the hump-shaped bead of the closure axially and to deform the hump-shaped bead radially outwardly towards the skirt of the closure:
(c) reforming the closure by diametral contraction of the root of the closure skirt above the threads of the container neck under "tight" reform conditions so that the said bead of the gasket acts as at least a partial side seal against the upper part of the neck of the container:
and (d) deforming the closure skirt radially inwardly against the threads of the bottle neck to form threads in the closure skirt corresponding to the threads on the container neck.

2. A method according to claim 1 wherein the hump-shape of the cross-section through the gasket bead is in the form of a truncated triangle having its base parallel to the end wall of the closure, a substantially straight radially inner side of the triangle being disposed at an angle of from 15° to 70° with respect to the plane of the closure end wall, and a substantially straight radially outwardly facing side being disposed at an angle of from 70° to 86° with respect to the plane of the end wall.

3. A method according to claim 2, wherein said truncated triangle is truncated so as to have a rounded apex.

4. A method according to claim 2, wherein said radially inwardly facing side of the triangular hump is inclined at an angle of 541/2° to the plane of the closure end wall, the radially outwardly facing side is inclined at an angle of 74° to the end wall, and the height of the hump above the general level of the central panel is 1.07 mm with a flat truncated top to the triangle.

5. A method according to claim 1, wherein said gasket is formed of a mixture comprising polyethylene and a styrene butadiene block copolymer.

6. A gasketted closure comprising a closure end wall having a generally cylindrical skirt depending from its periphery; and a gasket moulded on the inner face of the end wall of the closure with a gasket profile comprising a circular central panel bounded by an upstanding annular bead which bead is spaced from the skirt of the closure by a foot portion of the gasket having a height substantially the same as that of the central panel of the gasket, the profile of the bead being such that, in an axial cross sectional view, the bead consists of a substantially trapezoidal or substantially triangular hump having its centre of area disposed closer to the skirt of the closure than is the centre of the base-line of the hump, with the radially inwardly facing substantially straight side of the triangular hump inclined at an angle of from 15° to 70° with respect to the end wall of the closure.

the radially outwardly facing side of the triangular hump being substantially straight and inclined at an angle of from 70° to 86° with respect to the said end wall of the closure, and the triangular hump having a truncated top.

7. A closure according to claim, 6, wherein said truncated top is in the form of a radiused apex of the triangle.

8. A closure according to claim 6, wherein said truncated triangular form of the gasket hump comprises a flat top edge to the triangular hump, thereby defining a trapezoidal cross section to the hump.

9. A closure according to claim 6, wherein said central panel of the gasket includes a series of concentric annular ribs.

10. A closure according to claim 6, wherein the hump has a height of 0.72 to 2.5 mm above the central panel and an area which is from 0.9 to 3.7 sq.mm.

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11. A closure according to claim 6, wherein the angle of inclination of the radially inwardly facing side of the triangular hump is from 30° to 541/2°
with respect to the plane of the closure end wall.

12. A closure according to claim 11, wherein the height of the hump above the general level of the central panel of the gasket is 1.07 mm.

13. A closure according to claim 11, wherein the inclination of the inwardly facing side is 541/2° and the radially outwardly facing side is inclined at an angle of 74° to said end wall.

14. A closure according to claim 11, wherein the internal diameter of the skirt of the cap blank is 27.35 mm.