Printed matter – Method – Identifying
Patent
1988-06-06
1990-05-22
Bell, Paul A.
Printed matter
Method
Identifying
283 92, 283 94, 283901, 283904, B42D 1500
Patent
active
049271806
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the application of photochromic markings to articles and in particular to labelling of articles and substrates with photochromic marks for security or validation purposes.
It is desirable in many commercial fields to provide validation or security markings to products or documents in order to make forgery or counterfeiting more difficult. Examples are records or tapes, spare parts for vehicles or equipment, cheques, bank books, credit cards and other security devices.
A variety of methods have been proposed for making security devices, such as identity cards, more difficult to tamper with. U.S. Pat. No. 3,755,935, describes the production of an identity card which incorporates a double-sided photograph laminated into a composite card and having overlaying security printing. The inks disclosed include fluorescent inks. Cards such as described in this U.S. patent are very expensive to produce and such costs would not be acceptable for the production of validation labels and security documents such as cheque books or credit cards. Furthermore, inks which merely fluoroesce in ultra-violet light can be easily formulated using standard optical brightners and do not present significant problems to forgers.
According to the present invention there is provided a method of marking an article or substrate with a mark or device which is made visible or is enhanced on exposure to U.V. light which comprises printing onto the article or substrate a photochromic ink containing a photochromic compound which is reversibly converted to a coloured form on exposure to U.V. light and reverts to a substantially colourless form in the absence of U.V. light and applying a superficial protective layer to said mark or device which protects the photochromic compound against degradation by atmospheric moisture and oxygen.
The invention also includes a security device in the form of a label, document or card which incorporates a mark or device which is partially or wholly invisible in light which does not contain a U.V. component, which comprises a substrate having printed thereon using a photochromic ink a mark or device and having a clear, superficial protective layer over said mark or device which gives protection for the photochromic compound against degradation by atmospheric moisture and oxygen, said photochromic compound being converted to a coloured form on exposure to U.V. light and reverting to a pale or substantially colourless form in the absence of U.V. light.
The selection of photochromic compounds which reversibly colour in U.V. light and bleach in artificial light or filtered sunlight makes it difficult for a validation or security mark to be reproduced by a counterfeiter. A mark can be made even more difficult to reproduce illegitimately by employing a mixture of photochromic compounds having different absorption spectra or by printing a device using one or more inks containing different photochromic compounds.
Suitable photochromic compounds for use in the present invention should be capable of colouring rapidly in U.V. light at a wavelength of about 350 to 400 nm and reverting to a colourless form in the absence of such radiation. A rate of colouring of up to about 60 seconds and a fade rate of not more than 2 to 3 minutes is desirable. For some applications, e.g. for credit cards, the photochromic compounds should be capable of undergoing a multiplicity of reversible colouring-fade conversions, e.g. several hundred and be sufficiently stable to operate for the normal life of the credit card, e.g. about two years. Other applications such as validation labels for products such as records, tapes and spare parts may be less demanding.
Photochromic compounds which are particularly suited for use in the present invention include fulgides and fulgimides of the kind described in U.K. Patent Specifications Nos. 1,464,603, 2,002,752 and in U.K. Patent Specification 2,146,327 and photochromic spiropyran compounds as described in U.K. Patent Publication Nos. 2,190,379 and 2,193,005.
The compound
REFERENCES:
patent: 3594933 (1971-07-01), Cooper
patent: 3628271 (1971-12-01), Carrell et al.
patent: 3640009 (1972-02-01), Komlyama
patent: 3755935 (1973-09-01), Annenberg
patent: 4444939 (1984-04-01), Postle et al.
patent: 4500116 (1985-02-01), Ferro et al.
PCT Application No. WO 83/00568, published Feb. 17, 1983.
Japanese Patent Abstract No. 60-79992, vol. 9, No. 223, Sep. 10, 1985.
Brettle Jack
Trundle Clive
Bell Paul A.
Plessey Overseas Limited
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