Optical: systems and elements – Holographic system or element – Authentication
Patent
1992-10-22
1994-06-07
Ben, Loha
Optical: systems and elements
Holographic system or element
Authentication
428913, 428915, 283 86, 283108, G03H 100, B41M 314, G09F 303
Patent
active
053194756
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND
1. Technical Field
The invention relates to a tamper resistant security seal, for example for sealing containers such as security pouches and the like which are used for conveying items of value such as banknotes, letters of credit and the like.
2. Description of the Prior Art
It is extremely important that any such pouches possess tamperproof or tamper-evident seals. Various attempts have been made in the past to make such seals.
Generally these seals are adhesive backed tape constructions which are applied under or over the edge of the pouch flap so that the flap is held in place against the body of the pouch in a firm and tamperproof manner. They can also be in the form of labels.
In recent years the use of metallised films has been replaced by the use of optically embossed metallised films, which have a holographic or diffractive image. Such a construction was recently described by Advanced Holographics in GB-A-2211760. The advantage of using holographic films is that their counterfeiting is extremely difficult. The construction of the general purpose tape is similar to tapes used for hot stamping, for example as described in GB-A-2129739.
Very generally these tapes consist of a supporting film, a wax release layer, and a coating of an embossable thermoplastic polymer which has been subsequently diffractively embossed. Vapour deposited aluminum is then applied with an optional protective layer. The adhesive is then applied from a coating solution. WO-A-88/05728 introduces the general concept of a holographic protective film having a wax interlayer. Then a general purpose pressure sensitive adhesive layer is applied which is in turn protected by a peelable release paper. In use, the tape is fixed to a substrate using the adhesive. It is difficult to copy or alter.
JP-A-63106780 also describes another general purpose holographic tape. The tape is designed with weaker bonding between a protective layer over the holographic layer and an adhesive layer than between a transparent film on which the tape is formed and the holographic layer.
Similar constructions are known for covering large areas of, say, carton card in which an holographic transfer foil is rolled onto the card to produce a card having a diffractive metallic appearance. Such transfer foils are not known to have been used for security pouch seals. However, they are of similar structure to the tapes mentioned above except that instead of a wax release layer the embossable layer is chosen to have release properties from the carrier film.
Searle (GB-B-2136352) discloses holographic seals in which locally embossed areas of thermoplastic polymer are covered by a metallised film which is then demetallised. This leaves areas which are unprotected by the holographic image which is undesirable in case forgery is attempted.
Dai Nippon Insatsu in U.S. Pat. No. 4,856,857 discloses transparent embossed holographic structures in which the holographic impression is supplemented by a partial appearance of the underlying surface which may be a photograph.
Makowka (U.S. Pat. No. 4,834,552) describes making tamper-evident seals for plastic envelopes. The seal is double sided requiring two adhesives and is concealed under the flap in use. Inspection of tamper evidence can only be by folding back the flap and looking at the edges. Paper or cloth having a porous structure is used to protect against low temperature attack.
The use of holographic effects for security purposes is thus well known. The fineness of optical embossing and the nature of the holographic image make it very difficult to alter such devices or manufacture them afresh.
The term "counterfeiting" may be taken to mean the copying of an article by fresh but fraudulent manufacture.
Holographic devices are counterfeit resistant and may be counterfeit indicating. It is relatively difficult to construct an holographic image by "copying" it on a holographic table even if one were available. Slight variations in image quality would also be readily detected in any copy because of the fineness of
REFERENCES:
patent: 4268983 (1981-05-01), Cook
patent: 4608288 (1986-08-01), Spindler
patent: 4834552 (1989-05-01), Makowka
patent: 5145212 (1992-09-01), Mallik
Patent Abstracts of Japan, vol. 12, No. 354, (P-761) [3201] 22 Sep. 1988 and JP, A, 63106780 (Toppan Printing Co.) 11 May 1988.
Jones Keith A.
Kay Ralph
Silk Adam J.
Ben Loha
De La Rue Holographics Limited
Juba, Jr John
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