Note: Descriptions are shown in the official language in which they were submitted.
4S~ :
This invention relates to sealing gaskets for container closures,
in particular to the configuration ~profile) of gaskets for threaded closures.
Container closures are provided with gaskets primarily in order
to prevent air from entering the container and/or loss of contents of the
container to the outside. They are especially important in closures for
containers which hold food or drink since conta~ination 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 is for the closing
of 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. Gne general type of threaded closure which has found
wldespread commercial acceptance is the in situ-threaded type: threads are
formed during or after the operation of closing the closure onto the container.
Generally, a closure which is initially unthreadcd is closed by pressure onto -
the neck of a threaded container. Further, lateral, pressure is then applied
to impart threads to the closure while it is on the container, the threads
formed in the closure corresponding to those on the neck of the container.
For example the threads may be formed with the aid of a roller. Closure caps
~, 20 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 produc-
ed by the so-called spin-line process. In the spin-line process a pre- -
determined quantity of a plastisol of polyvinyl chloride is metered into a
closure; the closure is spun rapidly about an axis through the center of *he
flat top of the closure so as to distribute the plastisol by the action of
centrlfugal ~orce, and the plastisol in the closure is then fluxed. The
;plastisol is a viscous dispersion of polyvinyl chloride in a plasticiser. It ~ -
is fluxed by heating it to a temperature at which the plasticiser is absorbed
30~ b~ the polyuinyl chlorlde to form a homogeneous mass, which upon cooling gives
~,
~L0~57
a rubbery solid.
The spin-line process, although commercially successful~ has
limitations. One limitation is that the profile of gasket cannot be satis-
factorily varied. It is desirable to be able to vary the profile of a gasket
according to the particular size of cap and dimensions of bottle employed.
Because in the spin-line process the shaping is effected by centrifugal force
the gaskets produced will inevitably gradually increase in thickness from the
centre of the closure to its periphery. Thus, if for a particular closure
one wants to increase the thickness of the gasket near the periphery, it is
necessary to increase the total charge of plastisol metered into the closure
. '
or to increase the centrifugal force applied. The former is disadvantageous
because it results in a gasket which is also thicker near the centre of the
closure; this extra thickness at the centre is not required and thus there is
a waste of the valuable plastiso]. The latter is disadvantageous because
the whole profile of the gasket is changed and plastisol may be thrown a
....
considerable distance away from the top of the closure along the skirt, a posi- ~;
tion where it is not required. Thus the relatively "fixed" profile of the
gaskets produced by the spin-line process is disadvantageous because of the
difficulty or lack of economy in making minor variations to the profile.
A second problem of the spin-line gaskets is that for at least
,:,:~ ~
certain closures of the above-described type a relatively large amount of
gasket is required to give an effective sealing performance.
Another problem of the spin-line process is that in large produc-
tion~runs it is difficult to introduce the gasket-forming plastisol sy~metri-
j~ ~ cally into the region of the centre of the closurej with the result that when
the closure is spun the sealing portion is not ~ormed consistently in the
shape desired.
~ Yet another problem is that the choice of materials used for the
gasket is limi~ed to those which can be formulated as a viscous liquid for
.: :
spinning~ such as a polyvinyl chloride plastisol.
- 2 - ;
`. ', '' ' ' ,.
~: .. '.: ' , .
f ~:
In our United States Patent Specification No. 3,883,025~ issued May
13, 19759 we have proposed certain gaskets of a different pro~ile from those
produced by the spin-line process. These gaskets are useful in the in situ
threaded container closure in general, and may be made by moulding. Considered
in their undeformed configuration, i.e. before the closure is closed onto the
container, these gaskets comprise a substantially flat central panel and an ad-
joining peripheral portion, the thickness of which is at all points greater
than the thickness of the central panel and which increases continuously and/or
stepwise radially outwards to the skirt of the closure.
To express this profile in another way, consider the closure in its
inverted or up~turned position, meaning the opposite way up to which it is seen
when closed onto a bottle. The peripheral portion of the gaskets of our aore-
said United States Patent Specification No. 3,883,025 extends to a point on the
skirt of the closure which is overall upwards from the central panel of the gas-
ket. Considered in the direction of increasing radius from the centre of the
closure ~the radially outward direction), the height of the peripheral portion
. .
above the central panel starts by increasing and thereafter either continues to
increase or remains the same.
The gaskets of our aforesaid United States Patent Specification No.
za 3,883,025 having the above-defined profile enable the above-described problems ;
; to be overcome, at least to a considerable extent. They do not require such
large amounts of gasket material. Since they are made by moulding, their pro-
file can be varied. It is easy ~o introduce the gasket-forming material into .
and form it centrally in the closure and a wide variety of different materials
` may be employed. However, caps utilising these gaskets often become cocked out
of their correct alignment when the closing head is brought to bear on them~
with the result that the cap is not closed at all or is closed in an off-centre
; ~ manner, thereby often ~ailing to give a satisactory seal.
The present invention is concerned specifically ~ith gaskets for in
3Q s _ threaded caps~ especially roll-on caps~ which are to be closed onto
, .-: .. :.
~3
,:
.''~, ' ': :' ,
57
the container by a "reform" operation. In this operation force is exerted
during the closing of the cap not only downwardly but also laterally of the
` skirt of the cap, so as to pinch the top of the skirt inwards. In other words, ~ -
- the diameter of the skirt of the cap is reduced so as to compress ~he gasket
between the top of the skirt of the cap and the side of the neck of the con-
. tainer. A "reform" operation of this type is described in British Patent
`I Specification No. 975,739.
:,
Among the general class of gasket profiles described in our afore-
'~'' .9~ ' ~-/fJi ~,d~ s~fes
A said ~ s~ Patent Specification No.3,8~3,~a~ certain profiles are described
as giving a good sealing performance when the cap is subjected to a reform
.?~ operation. We have now found certain other profiles within this general class
which not only give a good sealing performance in this operation, but possess
another advantage not enjoyed by the general class or by the profiles speci-
' fically disclosed for use in the reform operation.
:~ The present invention provides a container having a threaded neck,
i~ a flat-topped rim adjacent said neck, a metal cap blank with a gasket therein
mounted over the threaded neck of the container in a pressing relationship
thereto, with cap blank having a reduced and deformed skirt diameter to com- :
press the gasket between the top of said skirt and the side of said container
~1 20 neck and to form threads in said skirt mating w.ith said container neck threads,
said gasket in said cap blank comprising a flat central panel occupying from
50 to 9~% of the internal radius of said cap blank and an adjoining peripheral
portion occupying the remaining 6 to 50% of the radius, the configuration of
said~peripheral portion when considering the cap blank in an up-turned posi-
l ~
tion relative to that which the cap occupies on the container with the peri-
pheral portion extending in a radially outward direction comprising:
~ ~ ~i) a first~part of relatively steep gradient upwards from the edge
J~ of the central panel making an angle with the plane of the central panel of
from 25 to 90 and having a radial length of from 5 to 30% of the radial length
of the whole peripheral portion;
.; .
~L0~ 7
(ii) an adjoining relatively flat step part o:E constant gradient
making an angle with the plane of the central panel of from 0 to 25 and having
~ a radial length of from 10 to 70% of the radial length of the whole peripheral
portion; .:
. ~iii) an adjoining corner part sloping upwardly, the height above
the plane of the step part being from 20 to 65% of ~he height of the top of
the corner part above the plane of the central panel, and ~ .
~iv) an adjoining final marginal part extending to the skirt . ,
either as flat step or upwardly and having a radial length of from 2 to 15% of
the radial length of the whole peripheral portion; said peripheral portion
having at least part of said flat-topped rim pressed against at least part of .: -
.~ the flat step part.
; A further aspect of the invention is the method of closing a con-
tainer having a neck which is threaded and a flat-topped rim, comprising plac-
ing a gasketted metal cap blank over the threaded neck of the container, pres- ...
' sing the cap blank down against the neck of the container, and whilst holding
:~ it so pressed~ reducing the diameter of the skirt of the cap blank, so as to .
~ compress the gasket between the top of the skirt of the cap blank and the
I side of the neck of the container, de.forming the skir~ of the cap blank so as .
to form threads therein which mate with threads on the neck of the container,
wherein said gasket in the cap blank comprises a flat central panel occup~ing
from 50 to 9~% of the internal radius o~ the cap blank and an adjoining peri-
.
: pheral pOTtiOn occupying the remaining 6 to 50% of the radius, the configura-
tion of the peripheral portionJ when considering the cap blank in an up-turned
position relative to that which the cap occupies on the container and when
~ considering the peripheral por~ion in a radially outward direction comprising
; ~; consecutively: ~ ;
.:,
) a firs~ part of relatively steep gradient upwards from the edge
~ ~ of the central panel which makes an angle with the plane of the central panel
.' 30 : of from 25 to 90 and which has a radial length of from 5 to 30~ of the radial
.. , ~ . .
''"
. , :`,: :
;:
.. ~ ,
, ' ., ~-
:: .
i7
length of the whole peripheral portion;
~ii) an adjoining relatively flat step part of constant gradient .
which makes an angle with the plane of the central panel of from 0 to 25 and :~`
which has a radial length of from 10 to 70% of the radial length of the whole .
peripheral portion;
Ciii) an adjoining corner part sloping upwardly, the height of which ...
above the plane of the step part is from 20 to 65% of the height of the top . :
of the corner part above the plane o the central panel, and
~iv) an adjoining final marginal part which extends to the skirt
either as flat step or upwardly and which has a radial length of from 2 to
15% o the radial length of the whole peripheral portion; and the closing of
the cap blank onto the neck of the container is effected so that at least part .. ~ :
~ of the flat area of the rim of the neck is pressed against at least part of
f the flat step part. ~ .
Preerred embodiments o the invention will now be described
with reference to the accompanying drawings, in which: ~
Figure 1 is a sectional view of a gasketted cap blank of the .. ~ ;
~ invention taken through a diameter, the cap being in an up-turned position . .
. rela$ive to its position on a container;
Figure 2 is an enlarged sectional view of part of a gasketted
. cap blank showing the configuration of the peripheral portion of the gasket; :. .
.. Figure 3 is an enlarged sectional view of a second configura- .
tion o the peripheral portion~ .~ ;: :
Figure 4 is an enlarged sectional view of yet another con- .`
figur~ation o~ the peripheral portion,
Figure S is a side view of the top portlons of a bottle neck
onto which gasketted cap blanks of the invention may be closed, and
Figure 6 is a side view of another configuration of a bottle
~; neck. ...
~ 3~ ~eferring now to Figure 1, a cap blank 1 shown has not yet
i - 6 -
been closed onto a container. It is made of thin aluminium, typically 0.008
to 0.012 inch (200 to 300 microns) thick, and will normally be lacquered on -
the inside and outside. (However, the presence of a lacquer or its nature is
not critical to the present invention). It has a flat top 3 from which depends
a skirt 5 bent over at its other end into a bead 6 clefining a mouth 7. The
gasket, having a configuration in accordance with the present invention, con-
sists of a peripheral portion 2 beginning at a radial distance x from the ~;
centre of the flat top 3 of the cap blank and adjoining a central panel 4.
The distance d marked is the maximum internal diameter of the cap blank. For
a cap blank having an external diameter of 28 mm., d is 1.092 inch ~27.7 mm.~. -
The diameter of the cap blank is not critical and the invention is applicable
to cap blanks having a variety of different diameters, including the commonly
employed bottle cap blanks of external diameters 26, 28 and 31.5 mm.
Some cap blanks have a knurled band stamped therein just above
:1 :,, .
the level of the gasket. A main purpose of this band is to stop the gasket-
ting material from being flung too far along the skirt in the spin-line process.
, .. .
This band is not needed in the present invention and so is not shown in
Figure 1, but it could of course be provided if desired. ~ -
Figures 2 and 3 show the peripheral portions 2 of two gaskets in
accordance with a first embodiment of the invention. These Figures have been
. ,
labelled geometrically to show distances and angles. We refer first to the
geometric labelling of Figures 2 and 3 to explain the invention generally.
~; The peripheral portion 2 of the gasket has an upper surface defined by the
Iine ABCDE.~ The first part AB has a relatîvely steep gradient upwards from the
edge A where the peripheral portion 2 joins the eentral panel 4. It may have
:~ ~ ` a planar or convex s~lope, preferably convex for ease of moulding. The angle .
is between 25 and 90. The radial length of the portion AB is from 5 to
30%, more usually 5 to 20%, of the radial length AW of the whole peripheral
portlon AE. In principle the radial distance AB could be greater, thereby pro- -
30~ ~ ducing a less steep gradient for any given height of B above the central panel,
, - 7 -
': , ~:,
- ` :
S7
but since part of the aim of the invention is to take advantage of every
reasonable economy which can be made in gasket material without adversely
affecting the quality of the seal, a length of more than 30% on the above
`. ` i ' !:
basis is of little practical interest. Because the gasket can be moulded it ``
is possible to make the gradient AB fairly steep and thereby economise on
gasket material. ~ `
The second step portion BC may be flat or have a slight upward
slope so that the angle ~ may be from 0 to 25 usually 0 to 15'~ and preferably ;
5-10. The radial length of the step portion BC will generally be ,~rom 30 to ~;
70, preferably 40 to 60 percent of A~. The optimum height XY of the step
portion above the level of the central panel 4 will depend on the resilience ~ ;
and toughness of the gasket material employed ,~ld may also depend on the nature
of the neck of the bottle. This will be discussed further with reference to
Figures 5 and 6.
The "corner part" CD will normally have a concave slope when
viewed as in Figures 2 and 3, but a planar or slightly convex slope might be `
appropriate for some purposes. The height of CD will vary according to pre
cisely how much gasket material it is desirable to have pressed into the corner
of the cap when the cap ~lan~ is closed onto the bottle. In general the dis- !','.:~'".. '~"
tance DX ~ill be fro~l 20 to 65% of the total height DY of point D above the
central panel.
The distance of point D radially from the centre of the cap cor-
responds to the radius of the moulding member employed to mould the gaskets.
Th~ls~the remainder of the peripheral portion, represented by DE is the radial
tolerance of the moulding operation. The dimensions of the portion DE *here- ~ :
fore have no great significance in themselves but DE will generally slope up-
,~ . .
~ wards e.g., as in Figure 2j or be flat as in Figure 3. The radial length of
!
~ ~DE may constitute between 2 and 15% of the radial length AW of the whole peri-
.
~ pheral portion. If the portions CD and DE both slope upwards so tha~ i~ is
. ,
impossible to discern a point D, the radial length DE may be assumed to be
- 8 -
~ ' ` '
:,
:-.
~0~ 7
the tolerance of the moulding member within the cap.
All the corners at points A, B and C are preferably rounded slight-
ly, for ease of moulding, but in principle they could be sharply defined.
Table 1 gives the dimensions applicable to some particular gasket~
ted cap blanks in accordance with Figures 2 and 3:
Table 1 ;
Figure 2 Figure 3 "~ :
inches (mm.) inches (mm.)
External diameter of closure1.102 f~28-00~n0~ 1.102 (28.000)
Internal diameter of closure d1.092 (27.737) 1.092 ~27.737)
Distance x 0.425 ~10.795) 0.400 (10.160)
atio x/d 0.39 0.37
. .. _.___ '
~adial lengths
~f AB 0.0223 (0.566) 0.0203 ~0.516) _
f BC 0.0521 fl.323) 0.0791 f2.009)
, _ ~ , . .~
f CD 0.0331 (0.841~ 0.0331 (0.841) ~ -
__ ~ _ - __ ____ . . ..
~f DE O.0135 ~0.343) O.0135 (0-34_}
, ~f AE (=AW) 0.121 ~3.073) 0.1460 ~3.708)
~eights
YZ (central panel) 0.006 (0.152~ 0.006 ~0.152)
~ 20 - -0.0416 CI-0s7~ - -- 0.0341 ~0.866) _
1 DX = 0.0336 C0.853~ 0.0336 ~0.853)
Radii of curva~ure
~t A (conc~ve) _ None 0.10 ~2.54)
~t B (convex) _ _ 0.27* (6.86) 0.015* ~0.38~ :M
; )f CD (concave) _ _ 0.040 (1.016) 0.040 f~l.076) ~ -
; ~ngles (degrees) -~
;~ o~ 10 . 10 :~ '. .'
,~ ~ ~ - ~ _ _ 50 _ 36 _ ;~
'~ ~ Gasket Material: Mixture of equal par~s by weight of polyethylene and
. ~ butyl rubber __ _
; ~ * The whole po~tion AB ~except for the concave radius at A in Figure 3) has
, .
a convex slope of this radius of curvature.
g_ ,
, :'
~L~4~4S7
In principle, any gasketting ~aterial may be employed in the
.:, ,.
present invention. A preferred material is a mixture comprising polyethylene, ;
butyl rubber, and optionally an ethylene/vinyl acetate copolymer. Poly-
ethylene/butyl rubber mixtures containing e.g., 40-70% by weight of poly- ;~
ethylene and 60-30% by weight of butyl rubber, are generally suitable. Gaskets
are preferably formed from these mixtures by cold-moulding as described, e.g.,
in our British Patent Specification No. 1,112,023, Australian Patent Specifica-
tion No. 420,653 and German Auslegeschrift 1,544,989. Other usable gasket-
ting materials include plasticised polyvinyl chloride and other vinyl chloride !
; 10 polymers known in the gasket-making art, other materials described in our
i British Patent Specification Nos. 1,112,024, and 1,112,025 and thermoplastic ~ -
,. ..
copolymers o butadiene with styrene, optionally in admixture with other
materials such as polyethylene. This class of materials is described in our
~, British Patent Specification Nos. 1,196,125 and 1,196,127. The gasketting
material is conveniently, but need not be, introduced into the cap in the
. ~ ~ . ..
form of a solid. It may be a plastisol of a vlnyl chloride polymer. Such a
~ plastisol can be moulded by the process described in our British Patent
`' ~ Specification No. 1,?39,927.
;`J~ The gasketting materials may of coursa contain any of the usual
additives such as a stabiliser, plasticiser, pigment, dye, filler, slip agent
or lubricant.
.,~ ~ , , .
~1 Al~hough, as explained above, a wide choice of gasketting mater- ~
~ !. - :~ -
~ ials~is available, certain practical considerations influence the choice of
-1 ~ : - ;
mat~erlals. To provlde a good gasket for an in sit~ threaded closure regard
must be paid~both to sealing performance and to the need to be able to un-
screw the closure easily from the container. In general terms a gasket made !~,,
of~a soft, relatively resilient, material will give an excellcnt seal but will
cause~the closure to be difficult to unscrew. Conversely9 a gasket made of
a hard, relatiYely unresilient materîal will not gi.ve a very good seal, but
1 ~30 ~ will allow the closure to be unscre~éd easily. It is necessary to strike a
' ~ ,
.
: :
,: : ,,
, j ~ .
balance between the two requirements.
We have now found that this balance can more easily be struckif the dimensions of the peripheral portion of the gasket, in particular of
the flat part (ii) and the corner part (iii) J are modified from those recom-
mended in the above-described first embodiment of ~he invention. In general
; terms~ the nature of the modification is to enlarge the corner part (iii)
both in the radial direction and in the direction parallel to the skirt of the ~ ;
cap. To do this it is necessary to reduce the radial length of the step part
(ii) somewhat. Too severe a reduction of the step part would reduce the -
; 10 resistance of the cap to cocking during the closing operation. The second
embodiment of the invention is therefore concerned with a delicate selection
,
of dimensions which alters the balance between sealing performance of the ~; i`-
gasket and unscrewability of the cap so as to permit relatively hard gasket
~~ .
r, materials to be used with better results, yet still mitigates or overcomes
;i problems of cocking during the closing operation.
;~j The second embodiment will be better unders~ood by reference to
:'!
~- ~ Figure 4 of the accompanying drawings which shows in section, taken through -
;~ part of the radius, the peripheral portion of a gasket of the invention within ~
; ~ . :
a cap blank.
Figure 4 has been labelled geometrically with the same reference
letters and numerals as for Pigures 2 and 3. Referring to the peripheral
portion 2 of the gasket, the first part AB is as described with reference
;'~ to Figures 2 and 3,~except that its preferred radial length is 15 to 30 per-
3~ ~ cent o the radial length AW of the whole peripheral portion AE.
The second step portion BC may be flat or have a slight upwa~d
slope so ~hat the angle ~ may be from 0 to 25 usually 0 to 15 and preferably - ;
;~ S~to 10. The radial length of the step portion BC will generally be at least ~ -
lO but less than 30~percent of the radial length A~ of the whole peripheral - ~-
~ pQrtion AE~ pxe~e~ably 15-25%. This is distinguished from the range o 30-70%
; ~ 30 recommended for the first embodiment. The optimum height XY of the step ~ ~
:' : . .
:
; ~ ' ' ,''
57
portion above the level of the central panel 4 will depend on the resilience
and toughness of the gasket material employed and may also depend on the
nature of the neck of the bottle, as discussed furt,her with reference to
Figures 5 and 6.
The "corner part" CD will normally have a concave slope when view-
ed as in the drawing, but a planar or slightly convex slope might be approp-
riate for some purposes. The radial length of corner part CD should be from
25 to 48% of AW. In a closure of internal diameter about 1 inch ~25-30 mm.),
corner part CD is preferably concave with a radius of about 0.045 to 0.06
inch (1.1 to 1.5 mm.). The height of corner part CD will vary according to
; precisely how much gasket material it is desirable to have pressed into the
corner of the cap when the cap is closed onto the bottle. In general the
; distance DX will be from 55 to 65% of the total height DY of point D above the
central panel ~compared with 20 to 60% in the first embodiment).
The ratio of the radial length of corner portion CD to the step ~;
portion BC should be at least about 0.8:1. It could be made as high as, say, ~-
, 4.7:1 depending on the precise combination of sealing, unscrewability and anti-
cocklng properties required. Towards the higher end of this range cocking
, problems may begin to re-appear, and the preferred range is about 0.8:1 to
1.7:1. Of course, if a soter gasket material were used the ratio could be
as low as 0.6:1, e.g. in a cap o internal diameter about one inch C25-30 mm.)
in which corner part CD is concave with a radius of about 0.04 inch (1.02 mm.). ;
However, the removal torque may then become rather high.
The portion DE is as described with reference to Figures 2 and 3.
~ All the corners at points A, B and C are preferably rounded
!
i ~ slightly, for ease of moulding, but in principle they could be sharply ;
defined.
The above-given dimensions ha~e been found particularly suitable
for gaskets made of mixtures of polyethylen~ and butyl rubber containing more
than 50% and up to 70% polyethylene, by weight; such gaskets being defined
: ' - -' '~'
- 12 - ;~
.' ;" " ~,
,
in our British Patent Specification No. 1,112,025. They are also suitable
for gaskets made of mixtures of polyethylene with a thermoplastic copolymer
of styrene and butadiene as defined in our British Patent Specification No.
1,196,125. These mixtures are harder than 50% polyethylene/50% butyl rubber
compositions and impart a lower removal torque to the cap. For example gasket
No. 1 of the Table below has a removal torque, measured after 3 days, of
about 20 inch-lb. (23.0 kg. cm.) when the gasketting material is 50% poly-
ethylene/50% butyl rubber and about 12 inch-lb. (13.8 kg. cm.) when the gasket-
ting material is 7~% polyethylene/30% butyl rubber.
It is possible to reduce removal torque by including a slip
additive in the gasket composition typically in a proportion of up to 1.5
weight percent based on the weight of the gasketting polymer. However such an
additive is often difficult to mix with the gasketting polymer, especially
if more than about 1 weight percent has to be added. An advantage of the
second embodiment of the present invention is that satisfactory removal tor- -
ques can be obtained ~ithout recourse to adding large amounts of slip additive.
Table 2 gives the dimensions of one particular gasketted cap
blank in accordance ~ith Figure ~ and, repeats for comparison the dimensions
set out in Tablé 1 for a gasketted cap blank in accordance with Figure 2.
. ...
. :`. , ~ '
' ' ; ''
: ~: '
': ~ '- '
. . ~. -
.,, , ~ .
. ` , .
..... ,..... .. , . : ..... . , ,,,, ,,, , , .: ~.
57
Table 2
Figure 2 Figure 4
inches (mm.) inches (mm.)
External diameter of closure 1.102 ~28.000) 1.102 ~28.000
. ~ . ~ ,_
Internal diameter of closure d 1.092 (27.737) 1.092 (27.737?_
Distance x 0.425 (10.795) 0.415 ~10.541)
_ _ ~ .
Ratio x/d 0 39 0 38
.:
Radial len ths
g
~f AB 0.0223 (0.566) 0.0323 (0.820)
~f BC 0.0521 ~1.323) 0.0315 (0.800)
... . : . .
` 10 ~f CD 0.0331 (0.841) 0.0537 (1-364)
~f DE 0.0135 rO.3431 O.OI35 tO.343)
_ ~ . . ~
Df AE t=AW)_ 0.121 ~3.073) 0.131 ~3.327)
Ratio of radial lengths of CD/BC _ 64 1.70
Heights
YX ~central panel) 0.006 ~0.152) 0.006 ~0.152)
~Y -0.0416 ~1.057~ 0.0416 rl.OS7)
. . . .: . .
.....
j DX 0.0336 ~0.853) 0.0545 tl.384~
'.i _ . . ~ ,
~ Radii of Curvature
i ~t A ~concavel None 0.10 r2.54)
, . . _ . ~ ,
~t B (Sconvex) 0.027* ~6.86)0.027* ~6.86)
~f CD ~concave 0.040 ~1-0~L____0.065 tl.651)
- ~ngles (degrees)
,., ' '' 10 _ 10 '' ' ':,
~ ~ 50 36 ~
, ~ . _ _ , . . .
* The whole portion AB (except for the concave radius at A in Figure 4) has
a convex slope of this radius of curvature.
~ Considerable variation is possible from the dimensions given in
.~ ~ Tables I and 2 but in general the overall weight of gasket material ~"film
~ weight") ~ill be less than the 450 mg. frequently needed for spun-lined
. . ~ .
gaske*s in this type of cap. A film weight as low as about 250 mg. can be
attained by the present invention.
'
, !, ` .
45~7 :
The method of closing the cap blank onto a container comprises
placing the gasketted metal cap blank (which is of course made of thin metal,
e.g., aluminium of thickness 0.008 to 0.012 inch [200-300 microns]) over the
threaded neck of the contalner, pressing the cap blank down against the neck
of the container, and whilst holding it so pressed, reducing the diameter of ^
the skirt of the cap blank at a position above the threads on the neck of the
container, so as to compress the gasket material between the top of the skirt
of the cap blank and the side of the neck of the container, and forming threads
in the skirt of the closure by deforming it at a position and in a configura-
` 10 tion corresponding to the threads on the neck of the container. The reduction
-; of diameter of the skirt may be effected by use of a closure head of suitable
shape, as described in British Patent Specification No. 975,739. This
operation will normally precede the operation of forming the threads.
The closures of the invention may be closed onto a variety of ;
:~ :
~ containers, but it is envisaged that the invention will be of use mainly for ~
::
caps closable onto glass bottles. The glass bottles may have necks of various ~ ;
types. One type common in the U.K. is shown in Figure 5. The neck has a re-
inforcing rîng 11 located below khe threads 12. If the peripheral portion of
the gasket is too thin the cap will be pressed too far onto the bottle, caus-
ing the head of the cap to hît the locking ring. This collision with the
locking ring will damage the cap and the seal. If the cap is pressed onto the
bottle slightly out of the correct vertical alignment, i.e., i there is cock-
ing, the lower end of the cap may strike the reinforcing ring. The flat step
part of the peripheral portion helps to prevent this from happening. The
. ~ .
invention is therefore of particular use in relation to containers having on
the neck a ring located immediately ~elow the threads which is of larger
diameter than the internal diameter of the mouth of the cap blank.
Figure 6 shows a "pilferproof" neck, the so-called "MCA finish"~
widely used in Germany, Belgium, Netherlands and l.uxembourg. The reinforcing
30 ~ ring in Figure 6 ta~es the form of a locking band 11 located below threads
!. '
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~ :
57
12 is thicker, butofsmaller diameter than the ring 11 in Figure 5. A cap
with a long skirt is employed, so that the skirt is closed over the locking
band 11 and into the area 13 of narrower diameter below it. The cap is then
pressed into the container neck in the area 13. A n~rrow band which is easily
fracturable is provided in the skirt of the cap in the region corresponding
to the locking band 11. It is then impossible to ~mscrew the cap from the
neck without causing fracture at the said narrow band.
The diameter t of the threads in Figure 5 is typically 1.063 or
1.088 inches ~26.00 or 26.65 mm.), the diameter e of the rim correspondingly
1.000 or 0.975 inch (25.4 or 24.8 mm.) and the height h ~rom the rim of the ~-
neck to the top of the reinforcing ring about 0.58 inch C14.7 mm.). Typical
dimensions for Figure 6 are: t = 27.65 mm., e 2~.92 mm. and h = 9.65 mm.
\ The rim of the neck has a flat top 14 which at its circumference
curves downwardly to meet side wall 15. The radially outermost edge of the
flat top (flat area) of the rim is marked by F. When the rim contacts the
gasket initially in the closing operation, places beyond F on the rim in the
radially outward direction should not contact the gaske~ at places radially ~;
in~ard of B within the cap blank.
The gaskets may be formed within the caps by moulding them, using
a punch. A quantity of gasketting material is deposited within the up-turned
cap which, when appropriate, may be pre-heated. It will normally be necessary
to h0at the gasketting material to soften it. It is 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 caps have
; general applicability. Although moulding is very advantageous, the invention ;
lies primarily in the configuration of the gasket. Therefore any method of
producing this configuration is in principle acceptable, and the invention is
not to be construed as limited by the process of making ~he gaskets.
The invention includes containers, especially bottles filled with
~; 30 beverages for human consumption, closed by caps of the invention. In the
':~ ' ' `
- 16 - ` ;
,
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S7
following examples tests are reported showing the excellent seals which can be
obtained. Percentages are by weight. ~'
EXAMPLE 1 ',
A cap blank of Figure 2 containing a polyethylene/butyl rubber
gasket and having the cap blank and gasket dimensions given in Table 1 and a '~ '
gasket film weight of 259 mg. was closed by a reform operation onto glass ;
bottles having the standard "continuous thread" finish shown in Figure 4. The
force of the closing head was 320 lb. ~145 kg.) and the side-roller force on
the skirt of the cap blank was 40 lb. (18.1 kg.). For comparison caps lined ~'
with 470 mg. of a spun-line polyvinyl chloride gasket were closed onto the `' '~
same type of glass bottles under the same conditions.
No problems of "cocking" occurred. ~ :
,~ Venting pressure tests showed that caps having both kinds of i' '
~, gasket had excellent resistance to the internal pressure of gases, such as i , ,
.i :: ,,.
are present in carbonated beverages, there being little difference between the '' '
, two sets of results Csee Table 3). Venting pressures were determined as '
follows. The caps were closed onto glass bottles with a hole cut in the - ~''',~
bottom. The necks of the bottles were immersed in a water bath so that the ,,' , ,'
cap was under water. The bottles were pressurised with compressed air intro- ' '
!
~, 20 duced through the hole in the bottom at a rate of 10 p.s.i. ~0.7 kg./sq. cm.) :`'''"~''~'
per 10 seconds, until bubbles appeared in the water indicating failure of the ,~
' seal or the pressure reached 120 p.s.i. C8.4 kg./sq. cm.). Attainment of this '~'"'"'~'"'
'~ pressure indicates a satisfactory seal.
''Table'3'-'venting'pressures (six sàmples~
Gap~of present invention: >120, 110, >120, >120
~ ~120, >I20 p.s.i. '~ - ''
'~ Cap containing spun-line >l?Q, ~120, 115, 115~ ',, ' '
'~ ' gasket: >120, >120 p.s.i.
(110 p.s~i~ = 7.7 kg./sq. cm, 115 p.s.i. = 8.1 kg./sq. cm; 120 p.s.i. = 8.4 ,'
~ kg./sq. cm.~
'~ 30 ~ T~is example shows that a far lo~er film weight is possible in '''
:
~ 17 -
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. ''' ' ':
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the present invention than that used in a cap gasketted with a spun-line
gaske~. Part of the 45% decrease in film weight is attributable to the use
of a material which is less dense than polyvinyl chloride, the specific gravity
of the polyethylene/butyl rubber gasket being 0.9 compared with 1.2 for the
polyvinyl chloride one. However, polyethylene/butyl rubber mixture is not
usable in the spin-line process and it is a particular advantage of the inven-
tion that by providing a sui~able configuration for a gasket which can be
moulded, it is possible to use polyethylene/butyl rubber. Moreover, the de-
crease in film weight attributable to difference in density of the gasket
materials is only 25% out of a total decrease of 45%.
EXAMPLE 2
:.
Pellets of gasketting material were moulded into gaskets in a 28
mm. roll-on bottle cap blank of thin aluminium. Three different main types
of gaskets were moulded, details as follows: ;
~ Designation Composition of gasketting material Configuration of gasket
- in weight % ;
A 70% polyethylene/30% butyl rubber Figure 2/Table 2
B 70% polyethylene/30% butyl rubber Figure 4/Table 2
.~ .
C 50% polyethylene/50% thermoplastic Figure 4/Table 2
styrenebutadiene copolymer -
"Cariflex TR 1102" -
D Polyvinyl chloride plastisol Spun-line ~i.e. accord-
ing to prior art ~ormed
by spinning the closure
about an axis through
its centre)
; Gaskets were moulded from compositions A~ B and C containing no slip additive
and various proportions of an oleamlde slip additive. `~
Removal torques were de~ermined after allowing the gaskets to age
for one day. Some samples were subjected to venting pressure tests to deter-
mine the strength of the seal. The results show that all the gaskets impart- ;
ed satisfactory removaI torques, i.e. good unscrewability, to the caps, but
gaskets A according to ~igure 2 did not give a satisfactory seal because of
the hardness of the material chosen. On the other hand, an excellent seal
and low removal torque were obtained from the gaskets B and C. ~It will be -
18 ~
. ' ~ ', ' ,';
57
understood that the Figure 2 gasket would have given a good seal if a softer
material had been used for the gasket. A slip additive would then be useful
to decrease the removal torque).
Results are shown in Table 4 below. The removal torqueSwere ob-
tained as an average of 10 samples, except in the instances otherwise noted.
Table 4
Removal torques after 1 day in i~ch lb.
(kg. cm.}
% slip ?~
ad~itive A B C D
O 10.5 C12.1)12.1 C13.9)10.5 C12.1) 9.2t C10.6)
10 0.1 7.9 ( 9.1)8.4 ( 9.7j7.~ ( 8.3)
0.2 7.9 ( 9-1)8.3 ( 9.6) 5.8 ( 6-7)
0.4 6.8 ( 7.8)7.4 ( 8.5)6.0 ( 6.9~ -
0.7 5.4 ( 6.2)7.3 ( 8.4) 4.9 ~5.6)
1.0 7.6 ( 8.8)8.~7 Cl~) 5.1 C 5~9) ~
1.5 4.4* C5.1)4.1 C 4~7
* average of 9 samples
~ average of 6 samples
Venting pressures of 2 samples of A Ccontaining 0.1 and 1.5% slip
:, :
' additive) were only 25 and 35 p.s.i. Cl.75 and 2.45 kg./sq. cm.) respectively, ~ `
Venting pressures were determined on 25 samples of B and C. Two samples of B
and one of C containing no slip agent withstood pressures of 110, 112, and 120
; p.s.i. (7.7, 7.8 and 8.4 kg./cm.2) respectively and the other 22 withstood
~ pressures of over 120 p.s.i. Cover 8.4 kg./cm.2).
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