Tape closure for a can end

A container end assembly comprising a container end, typically metallic, with a pour opening therein; a coating over the container end comprising a carboxyl group-containing vinyl chloride/vinyl acetate copolymer composition, and a pressure-sensitive adhesive tape bonded to the coating which forms a bond thereto which is greater than that between the coating and the metallic container end, such that upon peeling of the tape from the container end, the coating delaminates in the area of the adhesive tape bond, and is removed with the tape, thus effectively masking the tape adhesive for tamper indication.

BACKGROUND ART 
This invention relates to a container end assembly for use on beverage 
containers having a pour opening in the end covered by a length of 
removable tape. More particularly, the invention provides an improved tape 
closure for container ends permitting clean opening of the container with 
a tape closure, as well as tamper indication because the closure cannot be 
resealed once opened. 
TECHNICAL FIELD 
There are a number of tape closure assemblies utilized in conjunction with 
container ends, which are taught to be alternatives for scored aluminum 
can ends having a metal tab which must be lifted in accordance with the 
score lines in the aluminum end itself. One such tape closure mechanism 
has seen commercial utility in the area of liquids, such as fruit or 
vegetable juices. In such a tape closure system, a can end contains 
therein a preformed pour hole which is covered by a tape tab, attached to 
the can end by means of a pressure sensitive adhesive. The can may be 
opened by simply grasping the tape tab and lifting from the metal end 
surface, thereby exposing the pour hole. One problem with such an assembly 
is that this system does not provide any indication of tampering. The 
pressure sensitive adhesive is contained on the tab closure, and is not 
masked by any other material. Thus, the tape closure can be resealed after 
opening, thereby providing virtually no tamper detection. 
In another tape closure system, the can end having a pre-formed opening 
contains thereon dual coatings, the first coating being an enamel, such as 
an epoxy, and the overlayer thereon being comprised of a polymeric 
composition such as a vinyl chloride/vinyl acetate copolymer. A tape tab 
is positioned thereover and attached by a thermoplastic adhesive which is 
in essence heat bonded to the can end. Upon removal of the tape tab by 
lifting same upward, the vinyl chloride/vinyl acetate or outer polymeric 
coating is removed from the underlying enamel coating, thus providing a 
degree of tamper detection. Such a system is taught to be utilized for 
carbonated beverage-containing cans. 
However, I am unaware of any current commercial system in use today wherein 
a can end having a pre-formed pour opening, utilizing a pressure sensitive 
adhesive-containing tape tab closure, can provide tamper detection. 
SUMMARY OF THE INVENTION 
In accordance with the invention, there is provided a container end 
assembly which comprises: (a) a container end, typically formed of a 
metallic material, which has an exterior surface and an interior surface 
and is formed with a pour opening therein; (b) a coating over at least the 
exterior surface of the can end, which is comprised of a carboxyl 
group-containing vinyl chloride/vinyl acetate copolymer composition; and 
(c) a pressure sensitive tape which is bonded to an area of the exterior 
surface of the coating which is circumjacent and covers the pour opening, 
the tape forming a bond to the coating which is greater than the bond 
between the coating and the metallic material forming the container end, 
such that upon peeling of the tape from the container end the coating 
delaminates in the area of the pressure sensitive adhesive tape bond. 
In this manner, when the container having the end assembly discussed above 
is opened, the pressure sensitive adhesive on the tape is essentially 
masked by the coating which is removed therewith, thus providing an 
excellent indication of tampering, because the tape closure cannot be 
resealed as with prior art pressure sensitive tape closure systems.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
More specifically, FIG. 1 illustrates can end assembly 10 comprising the 
metallic can end 11 having a pre-formed pour hole 12 therein, illustrated 
by dotted lines under tape closure 15. Tape closure 15 comprises tape 16 
adhesively secured to can end 11 over pour hole 12, and grasping member 17 
for use as a manual gripping area for removal of tape closure 15 from can 
end 11. 
FIG. 3 illustrates can end 11 of assembly 10 which comprises metal 13 
having the coating of my invention 14 on the outward surface thereof. Tape 
closure 15 comprises tape backing 18 and pressure sensitive adhesive 19, 
with masking layer 20 covering or masking adhesive 19 at grasping member 
17, thereby preventing adhesive bonding of member 17. Tape 16 is 
adhesively bonded to can end 11 at least at areas surrounding pour hole 12 
to thereby effectively seal can end 11. 
FIG. 4 illustrates the partial removal of tape closure 15 from can end 11 
wherein coating 13, which had been adhesively bonded to tape 16 by 
pressure sensitive adhesive 19 is removed from metallic layer 13 as tape 
closure 15 is lifted from can end 11. FIG. 2 illustrates can end assembly 
10 after complete removal of tape closure 15. The portion of coating 14 
under adhesive layer 19 and bonded thereby to tape 16 has been removed 
with tape 16, while remaining in areas not covered by and adhered to tape 
16. 
Thus, adhesive 19 has been masked or rendered non-adhesive over the entire 
surface of tape 16, and tape closure 15 cannot be readhered to can end 11. 
Can end 11, in addition to my coating 14, can comprise bare metal, such as 
tin-free steel, tin-plated steel or black-plated steel. Such bare metal 
surfaces should be free of adhesion-inhibiting materials such as oil, 
etc., before application of coating 14 thereto. In addition, an enamel 
coating (not illustrated), such as an epoxy, can be applied onto the bare 
metal prior to application of coating 14 thereto. 
My invention relates to the use of a carboxyl group-containing vinyl 
chloride/vinyl acetate composition for preparation of coating 14. This 
composition provides the necessary adhesion characteristics allowing for 
removal thereof by conventional pressure sensitive adhesives typically 
used in tape closure can end assemblies. 
By the term "carboxyl group-containing vinyl chloride/vinyl acetate 
compositions" is meant that the vinyl copolymer itself can be modified by 
addition of carboxyl groups to the backbone thereof, or a carboxyl 
group-containing compound can be simply added to a solution of the vinyl 
copolymer to provide a simple mixture. In the latter case, the carboxyl 
compound must be compatible with the vinyl copolymer in the sense of 
allowing a homogeneous uniform mixture to be formed. 
Examples of suitable carboxyl group-containing compounds include carboxylic 
acids such as acrylic acid, crotonic acid, etc. 
In general, the adhesive and cohesive characteristics of the 
tamper-indicating tape closure system require that the adhesive force 
between pressure-sensitive adhesive 19 and coating 14 be greater than the 
adhesive (or cohesive) force between coating 14 and metal (or enamel) 
surface 13. Besides carboxyl functionality, molecular weight of the vinyl 
composition and the coating thickness of coating 14 are important 
parameters. For example, as the molecular weight of the composition 
increases, tensile strength thereof similarly increases, and thus coating 
thickness shall be reduced to maintain proper adhesion characteristics. 
The invention will now be more specifically defined through the use of the 
following non-limiting examples, wherein all parts are by weight unless 
specified. 
EXAMPLE 1 
A solution was prepared by dissolving 5 parts of vinyl resin "VMCC", 
commercially available from Union Carbide, which is taught to be a 
copolymer containing 83 percent by weight vinyl chloride, 16 percent vinyl 
acetate, and 1 percent maleic anhydride, having a number average molecular 
weight of 15,000, in 95 parts of a solvent mixture containing 
isophorone/methyl ethyl ketone/toluene in a 1:5:15 weight ratio, 
respectively. A sheet of approximately 10 mil thick tin-free steel plate 
was dip coated with the solution to provide a coating thickness of about 
0.05 mil after drying at 150.degree. F. for 10 minutes. Similar results 
have been obtained utilizing a Mayer rod with 30 lines per inch. An 0.5 
inch wide piece of "Scotchtab" Brand Closure Tape, a commercially 
available pressure sensitive adhesive tape used in providing tape closures 
from the Minnesota Mining and Manufacturing Company was adhered to the 
vinyl surface, after which the vinyl coating was effectively removed from 
the tin free steel plate by grasping the tape and lifting upwardly from 
the plate surface, thus providing distinct tamper indication by the 
inability of the "Scotchtab" tape to be readhered to the steel plate. 
EXAMPLE 2 
A conventional tin-plate can end, typically utilized for containing juice 
products therein, was coated with the solution of Example 1, again by dip 
coating. As in the previously example, the carboxyl group-containing vinyl 
coating was separated from the tin-plated metallic surface upon lifting of 
the "Scotchtab" tape therefrom. 
EXAMPLE 3 
A prepunched juice can end containing a coating of a conventional epoxy 
phenolic thereon (a typical enamel coating utilized with can ends 
containing product to be consumed) was dip coated with the solution of 
Example 1. The "Scotchtab" tape was then sealed to the can end around the 
pour hole area. The vinyl coating was again separable from the enamel 
surface upon removal of the tape tab by lifting therefrom.