Paper making and fiber liberation – Processes and products – Safety – identification and fraud preventing paper
Patent
1997-09-10
1999-02-09
Silverman, Stanley S.
Paper making and fiber liberation
Processes and products
Safety, identification and fraud preventing paper
162134, 162135, 162136, 162137, 283 57, 283 73, 428211, 427361, D21H 1924, D21H 2140
Patent
active
058689028
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/6B96/00562 filed Mar. 11, 1996.
BACKGROUND OF THE INVENTION
Field of The Invention
This invention is concerned with paper for security documents, and more particularly to those documents which are subject to considerable amounts of handling such as banknotes and driver's licenses.
It is important that security documents, e.g., banknotes and drivers' licenses, be durable; in other words, resistant to tearing, fold damage and soiling. Moisture and chemicals absorbed by such security documents during handling can lead to physical degradation. It is desirable that the substrate for such security documents be resistant to absorption. And it is, of course, a prime requirement for such security documents that the print which is applied to the substrate should adhere well, especially under severe conditions involving mechanical abrasion or accidental laundering.
The Prior Art
Security documents of the kind with which this invention is concerned incorporate one or more visible security features to prevent or deter counterfeiting. Included in the security features which may be used are watermarks and security threads present in the paper. Security threads may be disposed entirely within the paper or may appear in so-called windows located between regions where the thread is positioned between the surfaces of the paper, for example as present in the Bank of England Series E banknotes. It is normal in security documents for the substrate to be of good quality to enable satisfactory embossing to be achieved, such as embossing produced by the known Intaglio printing and to ensure good wear properties.
Previous proposals to provide paper for security documents which have good soil resistance and durability have involved the use of coating compositions which incorporate a pigment together with a binder such as an elastomeric binder. It is also known generally that various polyurethane compositions can be used on a wide variety of substrates to provide coatings which have a protective effect of one kind or another; amongst such uses, polyurethanes have been employed as a varnish for wood or other substrates. Also, it is know from European Patent EP-B-189945 to use polyurethane compositions as sizings for paper.
In the case where a coating composition involving a pigment is used for the production of security paper, e.g., as in PCT application No. WO91/12372, such pigment usually has a benefit in providing micro-porosity or roughness which enables satisfactory ink keying to be achieved. However, there is a serious disadvantage resulting from the presence of a pigment, namely that a security feature such as a watermark or windowed thread present in the substrate is to some extent obscured.
Pigmented coatings are inherently weak resulting from the presence of the pigment which causes the binder to be less firmly attached to the substrate in specific locations.
Usually, when pigmented coating compositions are used, the coating step takes place after the paper has been produced, and this involves the disadvantage of having to dry the paper before application of the coating composition. The prior specification EP-B-189945 refers to sizing, and it will be noted later that the present invention is concerned with the use of a polyurethane composition applied to security paper after the paper has been sized with a natural or synthetic sizing agent. Furthermore, it is an essential feature of the coating composition of this invention that no pigment is present so that there is no obscuring of any security feature. However, as will be described below, various functional additives may be present in the polyurethane coating provided that the opacity of the paper is not increased by more than 1%.
The present invention has resulted after extensive investigations by the inventors with the object of producing security documents which have enhanced durability and resistance to soiling.
SUMMARY OF THE INVENTION
According to the present invention there is provided a method for producing security pape
REFERENCES:
patent: 3880706 (1975-04-01), Williams
patent: 4462866 (1984-07-01), Tooth et al.
patent: 5232527 (1993-08-01), Vernhet et al.
patent: 5660919 (1997-08-01), Vallee et al.
International Patent Publication No. WO 91/12372, issued 22 Aug. 1991 to A. Vallee et al., for "Sheet for Protected Documents Having High Printability and High Handling Resistance."
Abstract of JP 06145598A (Dainippon Ink & Chem. KK) entitled "Polyurethane Coating Agent . . . for Coating Plastic Films or Sheets".
Foulkes Jonathan Paul
Howland Paul
Fortuna Jos'e A.
Portals Limited
Silverman Stanley S.
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