Flexible bags – Tamper indicating
Reexamination Certificate
1997-12-29
2001-08-07
Pascua, Jes F. (Department: 3727)
Flexible bags
Tamper indicating
C383S084000
Reexamination Certificate
active
06270256
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to bags formed of sheet material and, more particularly, to a tamper evident bag which is a security bag exhibiting a visible indication if an unauthorised attempt is made to gain access to the interior of the bag.
BACKGROUND OF THE INVENTION
It is known, for example, in financial institutions to use such bags to transfer sums of money between departments- A variety of different tamper evident bag designs are available, including that disclosed in EP-A-0 396 428, as illustrated in
FIG. 1
of the accompanying drawings and described in detail below.
A problem which arises with such bags is that the adhesive used on the tamper evident closure portion, which is used to close the bag and seal the access opening, fails to work adequately, if wetted, and the bag can be opened without visibly affecting the tamper evident closure portion.
The surface tension of all presently available substances which are used in pressure sensitive tamper evident closures, to seal such bags, is approximately 32 Dynes cm
1
. Therefore, the wetting of the closure with water, which has a surface tension of approximately 70 Dynes cm
1
and a low viscosity, is not an insurmountable problem. This is because the majority of the water used will be ejected by the action of pressing the closure to the bag. Also, due to its higher surface tension the water which is left will form droplets instead of smearing along the length of the closure, and will only cause localised failure of the seal. However, saliva, which has a surface tension of approximately 30-32 Dynes cm
1
and a much higher viscosity than water, will not be ejected by the action of the closure and will smear over the latter thus preventing adequate sealing of the bag.
Therefore, presently available tamper evident bags have the disadvantage that someone can pretend to seal the bag, but lick it beforehand, thus preventing sealing of the bag and enabling unauthorised access to the interior thereof.
It is an object of the present invention to address the aforementioned disadvantage of presently available tamper evident bags.
One apparent solution to this problem is to form a bag from a material with a reduced effective surface tension such that saliva will not smear on the bag and will not cause failure of the seal along its entire length. However, as discussed above the lowest possible surface tension of the material used on the closure to seal the bag is approximately 32 Dynes cm
1
. Therefore, the closure will act as a medium to smear the saliva, when pressed against the bag, and will thus prevent complete closure and sealing of the bag.
SUMMARY IF THE INVENTION
A solution is provided by the present invention, according to which there is provided a bag formed of sheet material and having an opening to enable access to the interior of the bag, a closure portion positionable over the opening, adhesive for securing the closure portion to the bag in order to seal the opening when the closure portion is positioned over the opening, and indicator means disposed between the closure portion and the bag when the closure portion is positioned over the opening and adapted to indicate wetting of the bag or closure portion upon attempted sealing of the opening.
Conveniently, the bag is formed from plastics sheet material which is folded to form first and second superposed portions which are sealed together along their free edges to form an envelope-like bag. The access opening may be disposed in the first portion and the closure portion may comprise a flap portion which is integral with or fixed to the sheet material of the bag. For example, the flap portion may be integral with the second portion of the sheet material of the bag so as to be foldable over the access opening. Alternatively, the closure or flap portion may be fixed to the first portion adjacent the access opening. It may be fixed to the sheet material of the bag by adhesive or heat welding. The adhesive for securing the closure portion to the bag may be in the form of a band of adhesive applied to the closure portion. Conveniently, a releasable cover strip is provided on the free surface of the band of adhesive.
The closure portion is preferably transparent or translucent and the indicator means is applied to the bag.
Preferably, the indicator means comprises a material having a surface tension less than or substantially equal to that of saliva. It may comprise a dye and a carrier material in which the dye is dissolved or otherwise supported.
The indicator means may present a coherent image on either the bag or on the closure strip which is disrupted by wetting. A message such as “open” or “tampered” may be printed on the bag, the message being hidden by the indicator means when not wetted and being revealed when the indicator means is wetted. Conveniently, the message and indicator means are both disposed on the bag. Alternatively, the message may be printed on the bag and the indicator means provided on the closure portion.
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Pascua Jes F.
Quatt Mark B.
Sealed Air Corporation
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