Plastic bottle caps

Plastic bottle caps of the snap-on type having tamper indicating means such as a tear band. The top wall of the top overhangs its side wall and the overhanging lip is filleted at an angle of about 30.degree. to increase the difficulty of removing the cap by hand without visibly affecting the tamper indicating means. Also, the cap has interior interrupted beads for snapping over the shoulder of the bottle neck and has ribs in the interruptions for adjusting the magnitude of the snap-on and snap-off forces. The cap is molded on a core having grooves for forming the beads and ribs. The cap may have a non-resilient gasket and a dished top so that it can exert pressure on the gasket. A foil seal having adhesive on one surface may underlie the gasket. After the cap has been applied to the bottle neck, the foil seal may be caused to adhere to the bottle neck.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to plastic bottle caps of the snap-on type having 
tamper indicating means (e.g., a tear band), particularly for lightweight 
plastic milk bottles. 
2. Description of Related Art 
Caps of this type are well known in the art. They have circular top walls 
and generally cylindrical side walls. See for instance U.S. Pat. No. 
3,338,446. 
Foil seals for container necks are shown in such patents as U.S. Pat. No. 
4,484,687 and the references cited therein. 
SUMMARY OF THE INVENTION 
The subject matter claimed in this application relates to a molded plastic 
cap having a top disk and cylindrical skirt and having a gasket liner of 
polyethylene and the like wherein a foil seal of aluminum or other 
material under the gasket adheres to the neck of the container to which 
the cap is applied. The to disk has a depressed central portion which 
engages the gasket.

All the figures except FIGS. 10 and 11 are drawn to the scales shown 
thereon. 
DESCRIPTION OF PREFERRED EMBODIMENTS 
The standard plastic milk bottle necks for use with snap caps have outer 
diameters of about 1.38 inch at the widest, and the outer diameters of the 
cylindrical side walls of the caps are correspondingly about 1.39 inch. 
The nutritional etc. information required for milk bottles is usually set 
forth in a label (e.g. of paper) secured to the circular to wall of the 
cap. To accommodate this information in readable form the industry usually 
employs circular labels having diameters of 13/8 inch. The operation of 
securing the labels to the top walls of the caps is not done with great 
precision and it is therefore desirable that the top wall have a diameter 
of at least about 1.5 inch in order to insure that the entire label will 
fit on said top wall. Accordingly, the top wall has been extended so that 
there is an overhanging lip or flange, as shown for instance in U.S. Pats. 
Nos. 3,927,784 and 4,166,552. This lip or flange aids in prying the cap 
off the bottle after the tamper-indicating means of the cap has been 
inactivated (e.g. after its tear band has been removed). The plastic 
material of the cap is flexible and the lip accordingly yields somewhat 
under the pressure of the fingers so that the amount of force that can be 
applied to the cap is limited and the cap cannot generally be removed by 
hand before the inactivation of the tamper indicating means. 
Making the lip rigid, as by filleting it at a 45.degree. angle (see 11 at 
FIG. 2), allows the hand to exert a larger prying force and increases the 
possibility of cap removal by hand even when the tamper indicating means 
has not been deactivated. I have found, however, that when the lip is made 
still more rigid by filleting it at an angle of about 30.degree. (see 12 
at FIG. 1), the opposite effect is obtained. That is, I have found that 
with the latter construction is instead becomes much more difficult to 
remove the cap by hand without visibly affecting the tamper indicating 
means (although it is readily removable by hand after the tear band has 
been torn away). 
The cap shown in FIGS. 1 and 3-8 comprises a top wall 13 and a wide wall 
14. A circumferential line of weakness 16 (See FIG. 6) divides the side 
wall into an upper portion 17 and a removable lower portion 18. The lower 
side wall portion has an inwardly projecting interrupted bead 19 for 
engaging under a shoulder 21 of the bottle neck 11 (see FIG. 3). The upper 
side wall portion also has an inwardly projecting interrupted bead 23 for 
engaging under an upper shoulder 24 of the bottle neck. For removal of the 
lower portion the latter has a tab 26 adjacent to which there is a line of 
weakness 27 which extends upward to the circumferential line of weakness 
16, so that when the tab is pulled appropriately the plastic of the cap 
tears first along the line 27 and then along the line 16. 
The to wall 13 overhands the side wall 17. Its outer diameter is about 11/2 
inches, while the outer diameter of the side wall is typically about 1.39 
inches. the overhang is filleted (at 12) at an angle of about 30.degree.. 
In one preferred form, the top wall has an annular plug portion 28 
depending therefrom. This plug fits into the mouth of the bottle to form a 
seal with the inwardly extending upper lip 29 of the bottle neck. 
The caps may be produced by injection molding in molds of generally 
conventional type (see FIG. 4) in which the mold cavity is defined by an 
end member or plate 31, a core 32 and a sleeve 33. The hot molten plastic 
is injected, typically, through a gate 34 leading through the end member 
31; it cools quickly to a solid self-supporting state in contact with the 
cooler mold elements. Then the mold is opened, i.e, the core and sleeve 
are moved relatively away from the end member and the formed solid cap is 
pushed off the core by an ejector pin 36 carried in the core. Since there 
are undercuts, etc., in the core the cap must expand somewhat when it is 
being stripped from the core. Such expansion is permitted because the core 
then moves, relatively, with respect to the sleeve (whose movement is 
suitably restrained as by springs, not shown), e.g., the core slides 
within the sleeve so as to bring the molded cap away from the sleeve. 
As shown in FIG. 6 the inwardly facing beads 19, 23 of the cap may be 
interrupted. One aspect of this invention relates to the use of ribs 37, 
38 in the interruptions. The mold core 32 (FIG. 5) has spaced relatively 
deep grooves 39, 41 (e.g. about 0.035 and 0.007 inch deep, respectively) 
to form the beads which engage the shoulders 21, 24 of the bottle neck and 
relatively shallow grooves 42, 43 (e.g. 0.01 and 0.003 inch deep, 
respectively) to form the ribs 37, 38 whose purpose is explained below. It 
will be understood that the heights of the beads and ribs of the cap 
correspond (approximately since there is some shrinkage of the plastic) to 
the depths of the grooves in which they are formed. Preferably the ribs 
are of smaller cross sectional area than the beads. 
When the cap is snapped on to the bottle neck it tends to expand 
circumferentially, when a bead slides into a shoulder of the bottle neck, 
and then contract when that bead snaps over that shoulder. The downward 
force needed to snap the cap onto the bottle depends, at least in part, on 
the resistance of the plastic material of the cap to such expansion. The 
needed downward force should not be so great as to damage the light-weight 
plastic milk-filled bottle on which the cap is being placed. It is 
desirable, however, that the upward force needed to unsnap the cap from 
the bottle be so great that it is practically impossible to do so by hand 
without damaging the tamper indicating means. I have found that I can 
adjust the magnitude of these forces by adjusting the heights (and widths) 
of the ribs between bead portions. The greater the cross sections of the 
ribs, the greater are the forces required to stretch the ribs during the 
snap-on and attempted snap-off operations. The adjustment can be made, for 
instance, by starting with a core having no rib-forming grooves and which 
will yield a cap for which the snap-off force is too low and then 
machining the rib-forming grooves progressively deeper and deeper until 
the resulting mold produces a cap which has the required characteristics. 
In the absence of the ribs the side wall thickness between bead sections is 
generally substantially the same as the general thickness of the side 
walls (usually about 1/40 inch). The ribs of course effectively thicken 
the side walls locally. In one preferred embodiment (illustrated in FIG. 
6), at least one of the interruptions between bead sections has at least a 
portion which is unribbed, e.g., there is no rib in the interruption 
through which the second line of weakness 27 passes. Typically that line 
of weakness (like the first) has a wall thickness of about 0.01 inch and 
is about 0.02 inch in width. 
The lines of weakness 16, 27 may be formed during molding, by outwardly 
projecting beads on the core 32, such as bead 44 (situated above grooves 
39, 42 and below grooves 41, 43) for forming the line 16 and a bead 46 for 
forming line 27. 
It will be understood that it is within the scope of the invention to 
employ the ribs in caps whose overhanging upper lip is not filleted at all 
or filleted at some angle other than about 30.degree., caps having no 
upper lip at all, etc. 
As previously described, the cap may have a plug 28 for sealing the mouth 
of the bottle. Instead of using a plug one may use a gasket. The surface 
to be sealed, at the mouth of the bottle, may be somewhat rough or uneven, 
as is the case with many blow-molded light weight milk bottles. In that 
case I prefer to use a gasket made of a material which will conform to 
such roughness by taking some local permanent set in response to the 
pressure between it and the rough surface. One example of such a gasket 
material is a "non-resilient" foam of, e.g., polystyrene about 0.02 to 
0.04 inch (e.g. 0.03 inch) thick. This material can be readily deformed, 
e.g., it will take, permanently, the imprint of one's fingernail; it is 
used extensively for cushioning wraps for bottles. 
It is found that such "non-resilient" gaskets often do not seal reliably 
when used in snap-on types of caps on conventional plastic milk bottles. 
In accordance with one aspect of the invention the reliability of the seal 
is greatly improved by modifying the shape of the usually flat top wall of 
the cap so that it acts resiliently on the gasket in an annular zone 
generally aligned with the underlying annular zone of contact of the 
gasket and the mouth of the bottle. As shown in FIG. 9 this may be 
accomplished by using a cap whose top wall 51 has a dished configuration, 
having a central substantially flat depressed portion 52 and an upwardly 
rising annular portion 53 (e.g., which may be of generally frusto-conical 
configuration) with the central depressed portion meeting the upwardly 
rising marginal portion roughly along a circular line or zone whose 
diameter is substantially the same as that of the lip 29 at the mouth of 
the bottle. The dimensions of the cap (including the position of the lower 
bead 19 and the thickness of the gasket 54) are such that when the cap is 
snapped onto the filled bottle the top of the gasket is pressed against 
that zone forcing it upward slightly; e.g., the portion 52 may be forced 
upward from an original position in which it is, say, about 0.03 inch 
below the outer marginal area 56 of the cap to a final position in which 
it is only about 0.015 inch below that area 56. 
As mentioned earlier, it is conventional to apply a paper label, having a 
diameter of about 13/8 inch (and a thickness of about 0.004 inch) and 
having a pressure sensitive adhesive underlayer, to the top of the cap and 
then press the label firmly onto the top by passing the labelled cap under 
a soft rubber roller having a diameter of say, about 3 inches. I have 
found that despite the dished configuration of the cap, the labels 57 are 
easily applied in this way and adhere very well in use, even though the 
configuration of the to of the labelled cap is changed (as described 
above) when it is applied to the bottle. 
The caps are typically molded of thermoplastic polymer such as a 
polyolefin. For use on lighweight plastic milk bottles (such as those 
described in the article in American Dairy Review, April, 1974, pages 36, 
38, 40, 60-62) low density polyethylene is found to be a very suitable cap 
material, e.g., Tenite polyethylene 18 BO grade A melt index 20. 
The cap whose top wall 51 has the dished configuration (as shown in FIG. 9) 
may also be employed with a gasket which is wholly or partially a foil, 
such as a thin metal foil (preferably aluminum foil having a thickness of 
about 0.001 to 0.002, or 0.003 inch, such as 0.0015 inch) or a similar 
hard thin material such as glassine paper. The foil of the gasket may be 
heat-sealed to the top of the neck of the bottle in conventional manner, 
as by induction heating in the manner illustrated, for instance, in U.S. 
Pat. Nos. 4,109,815; 3,767,076; 2,937,481; and 3,815,314. The gasket may 
be of the composite type, such as a conventional type comprising a lower 
layer (having, e.g. a thickness of up to about 0.005 inch such as 0.002 
inch) of an activatable adhesive, preferably a heat-activatable adhesive 
(e.g., a wax, such as petroleum wax, or a thermoplastic polymer such as 
plasticized polyvinyl chloride) located under the foil, so as to serve to 
adhere the foil to the top of the neck on heating. Overlying the foil 
there may be a backing layer (having a thickness of up to about 0.02-0.03 
inch or more of, e.g. chipboard, paper, foam, etc.) which may be held to 
the top wall 51 of the cap in any suitable manner (e.g. by adhesive or 
mechanical means) so that when the cap is initially removed from the neck 
the backing layer remains in the cap while the foil remains adhered to the 
top of the neck and seals the mouth of the neck until the foil seal is 
broken and removed by the user. The backing layer then serves as a gasket 
for subsequent reclosure of the bottle by the cap. It is often convenient 
to have the backing adhered to the foil by means of an adhesive layer 
(e.g. of wax) which is so weak that the backing (held to the cap) 
separates from the foil (adhered to the neck) when the cap is initially 
removed from the neck. 
When the caps containing the foil liners are initially snapped onto the 
necks of the bottles, the pressure exerted by the presence of the central 
depressed portions 52 of the caps acts relatively uniformly on the foil 
liners, promoting the consistent formation of a seal. In contrast, the use 
of the snap-on caps having a substantially flat top wall (without a plug) 
instead of the dished top wall often gives inconsistent and incomplete 
seals; this is a significant problem at present, particularly when the 
backing layer is relatively hard, e.g. chipboard. 
FIGS. 10 and 11 show variations of the top wall configuration with 
depressed portions 52a and 52b for the same purpose. In these variations 
the innermost portion (58a or 58b) of the top wall may be in substantially 
the same plane as the outermost portion of that wall; the depressed 
portion (52a or 52b) is in an annular zone between the innermost and 
outermost portions. 
It will be understood that the caps having depressed resilient portions in 
their top walls may be employed with bottles of any suitable material 
(such as plastic or glass) and with bottles which do not have inturned 
lips (such as lip 29 in FIG. 9) at the tops of the bottles. Also such caps 
need not be formed with an overhanging lip or flange at a 30.degree. angle 
as illustrated in FIG. 9; instead the flange may be of the type shown in 
the previously mentioned U.S. Pat. No. 3,927,784 or in U.S. Pat. No. 
4,166,552 or there may be no such flange. 
It is understood that the foregoing detailed description is given merely by 
way of illustration and that variations may be made therein without 
departing from the spirit of the invention.